Welp, seeing as you're struggling to get in the replies. I'll chuck in my useless opinion. The fan you linked up, is in my opinion, a rubbish choice. Think more about the idea of rigging up some PC Fans to it, like the ones you get venting air outa the pc box when it's just... y'know.. a pc.
Don't fret too much about the circulation inside the box, although a bit of movement in there is a good thing. Think more about venting it out of the box, ideally in a place where you can potentially wack on a carbon filter to cut down on the smell if there is any.
I'm no good with lights, but someone above mentioned that the light you've chosen needs a ballast. They're more expense, plus they get pretty hot. Seeing as you're currently doing things with a desk-lamp, I'm gonna assume you're around the same kinda grower that I am... ie... A little knowhow, a lot of passion, and not the biggest wallet in the world. Have a look in the CFL forum, and through some of the posts in this forum, there's a lot of Compact Flourescent Light growers in here, that've been packing them into PC Cases and coming out alright. I count myself in that batch, I went from seed to crop (cropping was today!!!) inside a tiny pc case, with nowt more than three of B&Q's finest Compact Floros. I am chuffed with what I've pulled from it, it's not huge, but it's a lovely smoke and it's not even cured yet.
As for the mylar, well, if you've got the cash handy, that stuff will almost definitely do the job. Just do like emannn said, and get something to stick it to the case with. I just painted mine white inside, as I just didn't have the funds for anything else.
Going back to the lights... Remember as well that you're growing inside a pc case.. Most bulbs are gonna put your temps through the roof and cook the living shit outa your plant. You then put that hand in hand with the surprise summer we're gettin here in Blighty, and you've got some shriveled girls on your hands in next to no time. CFL's are cheap, they don't put out hardly any heat. This means you can keep them really close to the lights too, without burning... meaning less stretch.
Anyways, I'm subbed, and will keep a good eye on ya... I'm off for the weekend, but will have a nose back in here when I get home again.