And... no. A heat mat won't put off more heat than one of those bulbs, but just make sure that the snake can't make contact with the mat (or bulb, for that matter). They... sometimes will burn. Badly. -_-
And... two lamps... eh. I don't think so. I tried it once, but found that it really made no difference in the snakes living and health. A night bulb is really all you need, just make sure your room is light during the day (but don't put the cage in direct sunlight... that's bad

And... humidity. Well, if you're going with a corn (which is an excellent choice

I honestly don't even monitor the humidity of my snakes unless they start getting dented eye-caps, shedding badly, breathing oddly, etc.
ALSO
Whatever you do... make sure you get a captive bred corn, not a wild caught or captive hatched. Seriously, man... captive bred is the only way to go with snakes. And stay away from chain pet stores, if you can. Like Petsmart, Petco, etc. They... well, they know nothing about reptiles and I've never had something from them survive for more than a month. Seriously. No. Joke. My ball python just died a month ago or so... after having it for two weeks. They said it was captive bred, but no. Once I got it home... I saw how it was infested with parasites.
I've also had many lizards die from those stores... so yeah. I have bought my last thing from those places. They suck. Chains need to get nuked. <_<
Either go to a mom 'an pop pet store if you have one around, look for a herp breeder in your area, or... if you prefer... order a snake online. Yes, you can order a snake online. I haven't done it yet, but I have many a friend who has and... it's actually really easy. And you get very healthy critters.

I'm planning on ordering a Cal. b&w banded king snake in the somewhat near future... just need to wait to spring cuz... it's too cold to do it here at the moment. XD
Here's a great site to look at: http://www.kingsnake.com/
Just hit classifieds to browse.
Also...
I can't recommend enough how important having a snake that eats frozen/thawed rodents is. Seriously... it makes a world of difference in it's temperament, as well as they're dirt cheap (dead food), and live mice/rats... are a hassle.
Check out this site: http://www.rodentpro.com/
I just ordered two years worth of food for my corn snake, and about 40 weeks worth of food for my boa from RodentPro for a grand total of $117. They're a wonderful site, quick... insanely healthy products (the rodents are just... so clean. XD)... and cheap.
I mean, look at it this way.
From a place like Petco it costs me $11 per rat for mah boa. And the rats are small. Really small.
Then, through RP... it costs about $4 for a rat, and it's a XXXL one. Which is huge. About double to triple the size of the ones at a place like Petco. o.o
It's the bottom one at this page: http://www.rodentpro.com/catalog.asp?pr ... rozen_rats
I say $4 because shipping raises the price.

Um.
Yeah.
I'm rambling. So easy to do about mah passion. XD
So yeah.
For a corn snake you'll want the overall temp to be about 75, with a basking spot of 80-83. Keep the humidity around 50%, but that's not a huge deal I find. just make sure to give the snake a little misting when it enters molting phase. That's what I do, and my little guy is very happy.

And my boa, for that matter.
