I second the method above for the Osaka achievement. It's much easier to play at Toyotomi and wait it out rather than trying to conquer everything and keep the Toyotomi in check with the Tokugawas. Could a Mod/Admin make an adjustment to the site's achievement guide??
Also, I know there's alot of discussion and irritation over the third horse and the four guardian achievements and I agree they're total bitches, but they seem to be random more than anything. I actually got my four guardian achievement after I lost a territory!!! Only way I was trying to be certain I had the right four guys was just to release all other characters, just have your lord and your four "guardians" in your entire Empire and you're guaranteed this achievement!!!
Slowly I grow to hate achievement hunting