I tried a couple of times with Tokugawa/Hard to conquer the Oda province, but whatever I tried it didn't work and they were taken out before i could get there. I was getting so annoyed that I just turned on the Imagawa instead!

Might not have been the smartest move but I did win the campaign in the end. The beginning went like this (all from memory so there might be some small inaccuracies/omissions):

1. Sell military access to whoever you can
2. Get trade going
3. Bribe the Oda army in your province, merge it with your army and kick the remaining Oda's behind
4. owari will be taken by others, so turn around, declare war on Imagawa and conquer them
5. Takeda attacked me next with a big stack at the eastern Imagawa province, but i managed to beat them and immediately marched on Kai, took it and made Takeda my Vassal!! I was very surprised they accepted, but they are a handy vassal: very aggresive keeping the other clans in the area busy. At one moment they had like 5 provinces but in the end they were destroyed by the Date
6. It seems Hojo was busy fighting in the east because all the units they trained in Izu and Sagami kept moving in eastwards direction (I guess I was lucky there). So Izu and Sagami were easy to take next.

At that point I had a solid basis from which to build up strength and work on my diplo. BTW all my early investments were in economy upgrades, ashigaru and Chi arts.