I've been keeping rats for 8 years, I've had over 30 (most at once was 12) I currently have 4.
They are very rewarding pets, really friendly & intelligent & fun. I've only ever had girls & a couple of neutered boys (already neutered from other people) My first few were from a pet shop, but since learning about 'rodent farms' I've only had rescues & 2 from a breeder.
I would suggest getting your first rats from a reputable breeder, where they will have been handled from birth & less likely to develop health problems.
The main issue with rats is that they have really sensitive respiratory systems, but this can be less of an issue with good genetics so find a breeder registered with NFRS (National Fancy Rat Society) So many of my rats have died from respiratory disease that my vet joked that I should have Baytril (small animal anti-biotic) on tap! Mammary tumours have also killed a lot of mine, poor things.
This is due to poor breeding (rodent farms which supply pet shops) & because most of them have come from poor environments where they've been neglected & had incorrect bedding/diet.
Do you know if you want boys or girls? Girls are a bit more active. Boys tend to be more 'cuddly' but I hate the smell of un-nuetered boy rats & the fact they have balls! My neutered boys have been on my favourites list :) sshhh, don't tell them I favourites!
You're right not to trust Pets at Home. I have known their staff to give out completely false information & being a complete rat nerd this infuriates me. They sell some cool stuff, just wish they didn't sell animals.
http://www.fancyratsforum.co.uk
This website is excellent. I used to spend hours & hours on it! i particularly like the 'habitat' section because it has cage layout ideas, which I think is one of the most fun parts. I dread to think how much money I've spent on cages, hammocks, tunnels, shelves, ladders, but it doesn't have to be expensive, mine have always been into pretty much anything - especially anything edible :)