First of all, I am 6'2" tall and 2## (we won't go there) pounds. My
GT3 works great for me, so you should have no problems with one.
Maintenance - Not much here. As mentioned, front-end allignment is
important. You should check the allignment when you get the bike
(your LBS should have done this already) and again after a break-in
period. I found that my bike was out of allignment after I had
ridden it for a couple of hundred miles. I trusted my LBS so don't
know if it was out when I got it.
Other than that, keep it clean and just normal bike stuff.
Equipment -
In my rack bag I carry a spare tube, a tire pump, tire changing
equipment, a small tube patch kit, two allen wrenches (they come
with the bike), a few zip ties, a bungy cord (for when you'r
shopping), and a small lock and chain. So far, haven't needed the
spare tube (knock on wood). Its nice that all three tires are the
same size. My riding buddy's bike requires that he carry two
different tube sizes.
Water, snacks, cell phone (if desired), and camera should complete
what you need, however your interests may dictate otherwise. I also
include ham radio gear so I can work 'bicycle mobile' while peddling
down the road. But thats my thing.
Oh also, don't forget the helmet.
Are you going to get one of the new redesigned GT3's?