Does a PS3 really need surround sound? In short, no.
Will surround sound really enhance games/movies on a PS3? Absolutely.
I think it all depends on what is important to you. Sound for me is as important as picture quality.
I have an Onkyo 606 and quad lite 5.1 speaker system and the difference between that and the TV speakers is mind blowing.
I previously had a Denon all in one surround system. When i got it it blew me away - it was the first surround system i had bought and the difference it made not just to games/movies but even normal TV just added hugely to the experience. When i upgraded to my current set up it was another massive leap in quality and i don't think i could go back to just using the TV speakers now.
So although it is not essential - the ps3 will obviously work without it - you won't be getting the best it has to offer without a surround set up.
My advice would be to set yourself a budget and see what is available. Then wait a bit longer to save up for what you really want!
Seriously, I would look at seperates - i have had both and the difference is worth the extra. Maybe get a decent amp to start off with and look for end of line deals on speakers etc. I know when i bought my quads that the new model was due out so i got them for £499 (RRP was £999).
On the question of full HD TV i have a panasonic TXP58V10B. It is full HD and looks simply stunning. I previously had a 720p set which looked pretty poor in comparison but tbh that is more (imo) to do with the panasonic being a much better TV than my previous one than it being 1080 rather than 720.
Various of my mates also have ps3s attached to either 720 or 1080 sets and some of the 720 sets look better than the cheap 1080 ones so i would definitely agree with Uridium on that front.