1) Don't even think about "the norm." "The norm" if for like 60% of the population to be overweight couch potatos!
2) All fast riders were slow riders once.
3) If you need to walk - walk. Especially up hills. No sense blowing your knees out. Soon you will flatten those hills and sail up them!
4) Your bike will be fine. I started 2010 at 305#'s on a road bike that i bought in 1985 - and it wasn't exactly top-of-the-line either. Went 2300 miles last year on it. Too many flats and a few broken spokes, but otherwise no problem!
I like that you posted this, because although I don't let it stop me, I still sort of feel funny when dressed in cycling stuff - and I've lost over 40 #'s! Seeing all the responses reminds me that I'm being foolish!