in terms fo going home, most breeders let babies go home at 5-7 weeks of age.
if you buy form a good breeder the babies will alreayd be used ot being handled and petted...though they tend to be fast and wiggly at that age even if they are well used to handling.
personally id suggest finding a breeder if possible.
http://www.afrma.org/
(links to area clubs and breeders) most breeders do ship as well weather permitting.
in terms of which sex...thats a personal choice.
ive had many of both...
my experience has been both make wonderfull pets.
the upside to having females is they lack testicles (rats have large testicles and some peple find it very offputting) and females urine and general odor is very mild. i personally dont find a well cleaned male rat cage smelly at all, but their urine is a little bit stronger than a females and males have a slight musy odor to them (reminds me of cooking popcorn or fritos.
females tend to be more active, more curious and more into everything...females are typically much more eager to learn tricks, ive never had a "snuggly" female however, the girls are always On the go!
males tend to be a little more laid back and lazy...while they can be taught tricks they dont seem to be as into it as the females and typically are much more into snuggles petting and generally being doted on by thier people.
personally ive NEVER had issues housing 2 male rats or 2 female rats together, but i always buy young rats, and i always go extreemly large on the cages, ive found both males and females will tend to scuffle if their cage is too small or they are "bored" so plenty of toys, out of cage time, and make sure each ahs their own space. i also tend to put 2 food bowls in the cage so they never feel the need to scuffle over the food bowl.
all rats will wrestle between eachother, this is very normal, pinning, forced grooming (some squeeking) but ive NEVER had any of my rats seriously fight or hurt eachother and over the past 20 yrs (got my first rats when i was 6) ive had many.
i LOVE rats as pets and once i get my own place and settled in id love to get a coule more ratties (dumbo rex)
personally...as pets, i prefer males.