Teensy = AtMega with a few small differences, such as an on-chip USB solution. Contact Paul Stoffregen, the maker @ prjc.com, he'll be able to help you answer whatever questions you may have. However, I'd expect the Teensy 2.0 to work for you w/o the need for 2 chips. Plenty of SRAM (8kb!), oodles of Flash (128kb!), lots of I/O and a great IDE to program in. What's not to like?