For PC? Mobile? I'd say 8GB should do it, in either cases.
For versions after v0.9.8 4GB MIGHT work on a good day, depending if the GPU shares memory with the default RAM, but for v0.9.2 I'd say 4GB will likely not work.
I mean you can always try it, it's not like it can do any harm. Always worth a try. And you can also try the less demanding version - run using hi_perf_and_BFP_intel_card_fix.bat from the game folder
Probably about the same. There are some really good optimizations coming with v0.9.8, those will improve performance and reduce memory consumption. All versions prior to v0.9.8 had a bug that reduced fps and made it choppy (something that had been there from the very beginning).
