OMG, what did I sign up for..??

I accepted the offer for the faculty position at "very awesome major university". I accepted it because I felt like with all the wonderful & abundant resources there, it would be easier for me to meet my research goals (and thus get tenure) compared to other places. I have recently learned (realized) that my own expectations are at least as high as, if not higher, than my future tenure committee at a very good school. I am ambitious, and want to do BIG SCIENCE... exciting science. I want to push my field.
This was my first interview, and it seems weird in some way to accept my first offer from my only interview. Kinda like buying the first dress you try on...? But this position in this department"fit" me so well!!
So now what?!?! I don't start till next spring/summer. I am currently finishing postdoc #2 and papers from postdoc #1. Smooth sailing, chill-out time right? When I start to think about what I signed up for.. assistant prof at very good school, I sometimes get attacks of FEAR, and I feel my breath taken away temporarily. Holy sh!t !! Can I really do this?? I got this fear attack yesterday when I got my first email from a potential student. This student is currently an MS student in my future dept. and is interested in doing a PhD with me, and wants to discuss this. I haven't responded, because I don't know what to say!!! Ack!! First of all, well I can't even organize thoughts into firsts. How do I decide..? I also find myself worried about this student's future career options, etc etc. Jeepers I am a mess over this.
I feel like I must not show any weakness or indecision, I must project leadership and confidence to the students. It's analogous to wild animals: if they sense fear (which they can, in body language for example) you're screwed. But at this point, I'm just trying to finish papers and then start writing grants, I do not know what to say to students yet..!!
Help..!!