Welcome to the forums!
Funny thing: when I got back into cycling it was right around my 24th birthday (back in July of aught-four)... and my birthday present to myself was a brand new Hardrock Comp.
You picked a great frame to start off with - 3 years of hard use and mine's still going strong.
Regarding meals - I usually to eat something small before I ride, and something small after a couple hours if it's a long ride. By small, I mean 200-300 good
calories - fruit, nuts, smoothies, granola bars, stuff like that. On a really
long ride, I'll stop for a light lunch. I don't like to exercise on a full stomach, so I hold off on big meals until I'm done riding for the day.
Everyone is different, but that works best for me.
'08 Bianchi San Jose
'06 Giant OCR C3
'04 Specialized Hardrock Comp