I'd like to ask about some stuff first, since I'm completely non-techie

My current board is ASUS P6T SE LGA 1366 Intel X58 ATX Intel Motherboard with a CORE i7 920 2.66GHz LGA1366 cpu.
- Since I work in resource demanding applications (Adobe After Effects for example), I'd like to get more RAM. I've got 8gb currently ( 2 x DDR3 4096MB PC1333 DUAL 2 x 2048 CL9 ) and I'd like to expand. I thought about getting another 8gb, but the specs say 24gb is the max amount and I'm thinking about maxing it out. There are 4 slots, so that would be a 2x4gb and 2x8gb configuration. Is that okay, or can it cause any problems? Any specific brands/products you would recommend? What about bus speeds? Most 8gb ddr3 are 1600mhz, and judging from the specification, my board supports it.
- I've heard that i5 and i7 processors are good for overclocking. I'm considering doing this, however, I have zero experience with it and I'm afraid I'll break something
Not sure if it's a good idea in this case. I'd also prefer not going into some crazy cooling solutions, getting a better CPU fan is okay though.
- If I'd decide to overclock, I might need a better PSU, right? I have a 500W one currently.
- Lowest priority: My current GPU is ASUS GeForce 9600GT 512MB DDR3/256bit DVI/HDMI PCI-E (600/1800). I think I might like to play some newer games soon (Got decent performance in Crysis 2 and DX:HR, but those aren't exactly new anymore
), and I think it doesn't really cut it now. Any suggestions? Having a gaming machine is low priority for me, so it would be great if I could get a decent upgrade without breaking the bank. Maybe somewhere around 180$ max? Would it be possible to find a card that would not only boost performance in games, but also in graphics software, rendering etc., in this price range?
- GPU related: how does SLI work? Could I buy a new GPU and keep my old GF9600GT for an extra boost? I've heard that both GPU's have to be identical to work in SLI.
Big thanks for help!