Eh, 40C is high-ish for idle, but I'm guessing you're using the stock cooler, which would explain that. 40-50C is fine though. Like I said, you're not stressing the CPU when downloading a game, so that's not a problem.
If you were running it 75C+ for hours on end, then I'd say you would need to be careful, but you won't be.
Uh, I run my computer for like 10 hours once, and it's still with 40c range. My CPU never goes to 70c. Max is about 65 when video editing. I think its okay. Also, what about power comsumption? I know it's stupid to ask but my parents are paying for the power bills, lol.