RAM spec does seem conspicuously absent. I assume that info is available to developers. I haven't gone to the development site to take a look yet, but once I do I won't be able to talk about it.
I would guess 512 MB of RAM. 256MB is what the 3GS has right now. However, a more enhanced version of the iPhone OS, would require more breathing room. It could have between 512 MB to 640 MB.
Not possible. It would create more heat and power consumption on the chip. Also, the chip looks very small for it to have a 1GHz capacity and be able to house the RAM. NAND modules are big.