My experience has not been as short lived as Hraf's, but have had my share of trouble keeping them alive! Most of the stock I've seen lately has been pretty poor and they don't seem to last longer than a few weeks. If you can find some that are wild caught, they seem to do better. IME they are pretty picky when it comes to water conditions and like warmer, acidic and very clean water! If the tank has not been running for a while, I wouldn't try it.
As far as guppies and rams go, no problem there. The rams will either stay near the bottom or roam all over, but are pretty peaceful. When spawning, they get a little terratorial. but nothing too aggressive. The 29 gallon should give the guppies lots of room to move away should they need to.
Now, your very last line throws in a little more with you having Corys as well. Corrys are bottom dwellers, same as the Rams will be if they start spawning and that's where trouble can occur. Since the Corys are pretty active and move all over, they seem to make breeding Rams 'nervous' or something and IME, it's always led to the Rams eating the eggs. Also, the Corys are usually more aggressive about eating the eggs than the Rams are about defending them, so they can get eaten that way. I've heard of others having trouble keeping Rams and Corys together, but I've never had that experience.
Also, I've never seen a Blue Ram get 3" long... closer to 2" when full grow. Bolivian Rams get a little bigger than the Blue Rams and can get 3 - 3 1/2 " long. A pair of those would be fine in your 29 also. They are much easier to keep and find good stock.
Best of luck,