one question:
WHY?
Gentoo is probably not going to have support for many hardware features on the Infuse. I would be particularly concerned that the radio won't work, and without network connectivity it would be pretty useless.
Additionally I don't know of any touch screen friendly window managers that will work with Gentoo, using Gnome, XFCE, EWM, etc would be pretty troublesome on a 4.5" capacitive display.
If you were doing it just for fun it seems like a better idea to use a cheaper device with a resistive screen so you can use a stylus with it. Maybe a Archos 5IT or something....