New Computer - Qs

(I tried abusing Google for my awnsers, but I either get lost in something irrelevent or it brings up about 100x Hardware Depot websites. This is my first computer, so i'm very much a noob.)

1)I would like to know whats the appropriate amount of cooling devices for a gaming computer, in general? I don't have the specs for my computer seeing as i'm not at that computer atm, but I can try and give a good idea:

It has a decent CPU (3.0GHz/included heatsink+fan), Graphics Card (400+ $ worth), and power supply (500ish range).
The case has two fans 80mm & 120mm. I don't plan to overclock, mostly because I don't know what it is, but it seems important from alot i've read. Ask for any other info if needed.

I'm worried that what's given won't be enough, or worse, will cause lasting damage to my computer (Computer is not put together yet). Should I look into more cooling devices?

2) Does leaving your computer on for extended periods (days) cause bad wear-and-tear?

3)I read alot about people describing the temperature of their computer, where can I find such info? Is it a program or hardware? Anal thermometer?

1. For a gaming PC, you will have at least four fans - one on the CPU, one on the GPU, and an intake and exhaust fan on the front and back of the case respectively (plus one or two fans in the PSU). Don't skimp on the CPU fan - the stock coolers are generally sub-par, but Zalman make great CPU coolers (they cost a bit more, but run quieter and cooler). A case with a chassis air guide is a good idea too (basically a blowhole in the side of the case with a plastic duct to allow cool outside air to be drawn directly onto the CPU fansink). You might want to replace the GPU cooler as well, but these tend to be better designed for the card in question. Also, don't be a cheapskate with the PSU - modern components are incredibly power-hungry, so you need one that can supply enough wattage AND keep that power stable (buying on wattage alone is not enough - better a good solid 400-450W PSU than a cheap-ass 550W one).

2. Perhaps. If it's cooled properly and cleaned regularly it won't harm it especially, but you might find the fans getting clogged and worn quicker. Switch it off when you're not planning to use it. Increased risk of damage from switching stuff on and off a lot is a more or less myth - it's a computer not a lightbulb - and you'll save money on electricity.

3. Temperature is monitored by small thermistors on the motherboard (and many come with extra plug-in thermistors that connect to pins on the motherboard, and you can position these around the case for more detailed monitoring). Truth be told, they're not all that accurate, but do serve as a handy guide.