first thing you think when you meet a really hot girl depends on how she comes across as a person. If shes arrogant or a bitch I know I don't want to go out with her so I don't hav to get to know her or let her know much about me, I just have to find out if she's interested in sleeping with me. If on the other hand she's got a good personality, there's a lot more thinking going on. You wanna find out if she has a boyfriend, get to know her, you wonder if you'd get on together, for some reason you don't think about seducing her but showing her your funny & genuine side, the man u could be with the right girl by your side. oh, & we wonder if the bra your wearing is padded & hope to god it's not!
Which leads us too your next question, I don't really know the answer, Froid would tell you it's to do with our need to be mothered! all I know is if they are the right size & shape, there is something irresistable about them, & they have more controll over men than they should!
Biggest turn-offs are: smoking, piercings, swearing, & too much makeup.
Growing facial hair is a primal thing, men sometimes don't shave it off to remind them of our animal instincts & that we are not completely tamed by the clean, organised society we live in today. I doubt you'll be able to relate to this tho.
Why do we think about sex? well, maybe it's all the testosterone we have in our body, or our built in need to procreate, or maybe just because its really good fun.
I'v probably told u way more than i shud have, but not all men think the same, so don't go thinkin u'v got us sussed any more than we we hav u :)
good luck.