1. Depends on your overall storage vs versatility needs. Smaller drives tend to be faster (99% of people wont notice the difference but people running mass file servers and such might). Smaller drives also mean less crap is lost if the drive fails. On the otherhand, a bigger drive means more space. You can still make partitions to split that 200GB drive into, say, 80GB chunks if you wish.
2. Suppose you leave a computer on all day (room temp ~20C) ... the end of the day the drive is pushin 50C ... pop in some cooling (even a basic 80mm case fan you tape/tie to the case or just plain point in the general direction of the drive) and the drive will be in the 30C range. I dont think the drive will incur damage or anything at 50C (or 60C as ive seen from time to time) and most likely the big motivator is personal preference. A simple fan should do the trick for most people ... if you're gonna be doing something like say a file/media/app-server and/or will have the machine on 24x7 you might even wanna get a "premium" fan which will knock the temps down to the 20-25C range. Watercooling is available but overkill for 99% of people
ya that helped alot thx. ill just get a regular fan then and ill get the big 200gb instead. My computer wont' be on 24/7....maybe ill leave it on all night to download stuff sometimes but thats it. Ill just slap a fan in my computer. THANK YOU!!