Basically I think you have to take a "eat or be eaten" approach with Oda. Clans like Hojo, Shimazu, and Uesugi have the option to tech up initially because they don't have too many defensible borders… for Oda this isn't really an option.

Initially, and unknown to many players, Oda just edges Hojo for the richest starting lands. This large koku output is great for a quick and crippling attack to your enemies so you can expand your borders and gain a solid foothold in enemy lands early on.

Yari Ashigaru can be built cheaper with this clan and the longer the game drags on the less effective these units will be especially against naginata, no-dachi, and warrior monks. This is all the more reason to attack early and use the Ashi's to your advantage.

First Season
Let's face it, bridge territories are a bitch to take later than sooner because they're so easy to defend with a decent-sized force.

• First step I did with Oda was attack Imagawa's bridge province of Mikawa.
  Taking this province early allows you to do two things: (1) You push Imagawa back and get the defensive advantage early on by controlling this territory. (2) You isolate your capital city of Owari by surrounding it with friendly territories.
• At the same time I began to build castles in several provinces and I started a large castle in Owari (you can also choose to build farm improvements in Owari but I chose a large castle. See 3rd season). Here's where I built the castles and why: (b1.) Mino - I plan to build an armory here later so this is a no brainer really. It's on my eastern front so I can filter troops quickly and easily to help defend Mikawa or I can attack northern and eastern provinces. (b2.) Kii - I plan to send troops westward to push Mori back and it gives me a +1 bonus for monks later on. I also chose Kii because it has access to the sea which means if I build a port here later on I can ship my +1 honor monks a further distance. Some may ask why I didn't choose Kawachi… my reasoning for this was because it has two borders to defend thus the possibility of losing was increased significantly.
• You should have enough koku left over from castle and/or farm improvement production to build units in Owari. Build Yari samurai now to compliment your abundant Ashigaru forces, because once you have all your spear dojos in place you'll be building lots more ashis and not too many Ysams.
• While your castles are in production start moving your remaining forces to the western borders of Harima. Don't worry too much about the Ronin, they don't become expansion minded until 10 years or so. Leaving one unit per province internally will suffice. I started loading up both Kawachi and Tamba with troops, this way I give Mori two targets to look at and if he decides to get greedy I'll drop in the back door and take Harima while he advances forward.

Second Season

• Your small castles are finished so build your spear dojos in your two provinces.
• The large castle or farm improvement is still in production so build some more Ysams in Owari and maybe some farm improvements in Mikawa and Kawachi to increase koku output in the future.
• Continue to beef up your western and eastern fronts for attacks in the near future. If Harima is weak take it but it most likely won't be.

Third Season

• Your spear dojos are finished so start churning out the cheap Ashigaru units. Move them east and west as needed so you can build up your fronts and prepare for some big battles in the coming seasons.
• Once the large castle or farm improvement is completed in Owari you have a choice. You can continue to make farm improvements, or you can build a Buddhist temple which would allow you to create monks by the 6th season. Even though they're expensive… coupled with a ton of Ashigaru, two or three monk units can wreak some major havoc on the battlefield early on.
• Assuming you had an average season or better you should have enough koku to start producing that all-important armory in Mino. If you don't, no worries just load up on Ashigaru and Ysams in the three spear dojo provinces and save the remaining koku for an armory next year.

Fourth Season

• By this point you should have a strong enough force to start pushing back Imagawa and Mori back by spring or summer. You can also choose to take Shinano but that place is a headache to defend and isn't worth the early trouble in my opinion. Let the computer fry it's circuits trying to hold that province.
• Mori should have started attacking the rebel province of Tajima which has weakened him in Harima. Move the forces from your two bordering provinces and take out Harima. If Mori's already taken Tajima no problem just leave a few units back to defend Tamba. If you don't think you have the force to do it just wait a year and you'll have more than enough Ashigaru to take it. Don't wait too long though, Oda's biggest advantage is large numbers of cheap units early on.
• Don't hesitate to take Imagawa's capital Totomi. It's lowland which makes it hard to defend, not too mention your ruthless daimyo Oda should be giving those Yari troops an honor bonus in battle. Again, if it looks risky… wait a year for reinforcements or two years for warrior monks. The earlier you can take that capital the better… or if it looks easy to take earlier on go for that as well.

Fifth Season

• Keep building Ashigaru and Samurai. Build farm improvements with your extra koku or save it for the monks that should be coming by next year.
• It is very important also to build a Tea House somewhere around this stage in the game. Shinobi will greatly increase the survival of your generals and more importantly heirs to the throne. Never leave your heirs or high-ranking generals in a province without having a shinobi shadowing him at all times. In my game I created them just in time as I was experiencing two or three ninja attempts every other turn. Shinobi will catch many enemy shinobi and ninja in the early stages and they will also serve as valuable mobile reconnaissance later on as you expand your empire.
• If you haven't already, you should be attacking Harima and maybe Totomi in the west and east respectively. (Remember this was based on the events in my game. If the opportunity isn't there don't do it… but chances are it will be)

Sixth Season

• The Buddhist temple should be finished by midyear so save 1000 koku for the warrior monks.
• You should have taken Harima by now with your two sets of outnumbering Ashigaru based armies in the west. With this front solidified you can pick and choose one of four Mori provinces to attack from while only defending two... Harima and Tamba. Mori should not have the forces to defend all four provinces so simply move most of your two armies ahead to take more land while leaving a decent sized force to defend the back province of Harima.
• If you haven't already started besieging Totomi, you should be by year's end with the overpowering warrior monks. This early in the game the warrior monks can help you overcome many things w/ your Ashigaru saturated armies.

Seventh Season and Beyond

• If the armory wasn't completed in Mino last season, it should be this year. Now you can start churning out naginata from Mino and monks from Owari. You probably won't be able to afford anything else so just concentrate on sending these units to your front lines.
• With Mori suppressed fairly well and Imagawa nearly flattened in the east, you might want to consider taking out the Ronin forces internally within the next two or three years. It was nearly impossible to take these territories earlier because the Ronin have a fairly large force of monks in both Yamashiro and Ise. You now have the monks and naginata to take these provinces so it's better to act now rather than waiting for the Ronin to go on the offensive… it will only cause headaches later on to come back and kill these forces when they become expansionist.
• After the Ronin are defeated you can move these forces west or east depending on where you need the most help… probably in the east where you should be engaging the last remnants of Imagawa or the beginning of the Takeda or Hojo clan at this point.
• Mori should be fading quickly so you may want to create troop producing facilities somewhere along the western lines so that you can use those forces to crush any Mori, or Takeda west forces on your way to engaging Shimazu or Imagawa west.
• At this point anything can happen; Uesugi can attack, Hojo and Takeda might kill each other or unite against you. Hopefully this guide will help you along in your quest to become Shogun of Japan with Clan Oda.