I've always found that everyone who's bought a small MIDI keyboard (25 keys) has always regretted it about a month later and wished they'd bought a bigger one. At least that's the case for three of my housemates. I'm actually feeling rather similar myself right now.
I'd only really get a small one for portability.
Also, on bells and whistles:
They're all very well, but at the end of the day I expect you'll find yourself not using a lot of them. On-screen control is just fine for most applications (although faders and pots are nice to have for a more tactile response, but many software synths won't be mapped to your chosen keyboard, and that's more hassle and time not playing). As long as the keyboard has keys, a pitch bend wheel, a mod wheel, and octave selection you should be fine. I'd also urge you to go out and try the keyboard you're about to buy because they tend to feel very different from one to the other. Some that look good on paper just fly straight off the wishlist the second you get your hands on em.
