1) About how much disk space is required for a minimal Gecko engine on the embedded system?
For Linux, I'd guess something around 12-13MB (the mZ numbers on http://tinderbox.mozilla.org/SeaMonkey/ are sort of measuring this; you may be able to shave off some more with the right build options). alecf or dougt could tell you more, since they're working on that stuff at the moment.
2) How much RAM is required for Gecko to operate?
This "depends", of course.... Dynamic footprint for rendering a large page can be as much as 20MB (eg loading http://bonsai.mozilla.org/cvsblame.cgi?file=mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp takes something in that range, last I checked). This is in addition to the static footprint of just having the libraries loaded. Most pages are a lot smaller than that, of course; I'd say that about 50MB RAM usage in a real-world browsing situation is "normal" for Mozilla proper; dropping the chrome may save 5-10MB off that....
Basically, I think the "64MB" requirement we list is unfortunately all too real at the moment.
4) Can Gecko use SVGAlib instead of X?
Not out of the box. There has been talk in the past about writing the glue code to make this work, but no actual results that I know of.
