Hey there ZoeHale,
Welcome. As someone who's kept mice for a few years, and someone who is also getting her first rats soon, I can tell you from my research that keeping rats will be much different than keeping mice. In fact, I'd say rats seem to have more in common (in terms of amount of responsibility) with ferrets, than mice. LOL
I will be happy to share some of what I've found. I know everyone else here will give you even better advice. Lessee. In no particular order, some considerations:
1) Males and Females are equally social, so just as you are doing, keep them in same sex pairs, or groups--or if they are neutered/spayed, you can safely keep them mixed sex.
2) Rats are prone to respiratory problems. Extra care will need to be made to keep them healthy, or to care for them when they get sick.
3) Cage: Aquariums are not a good choice. There is not enough ventilation to keep their lungs healthy. Also, you will need to make sure the cage bars are small enough to prevent escapes. Smaller females and juveniles are notorious escape artists. You should plan on spending between $70-150 on a proper cage, though some folks can find them cheaper occasionally on craigslist/ebay/freecycle or through rat community swaps.
Examples of good cages for your needs:
Martins Cages: http://www.martinscages.com/products/cages/rat/
The best choices are the R680, R685, or R695. Avoid their 'aquarium toppers', as the rats will not use the bottom level, and it is horrible to keep clean.
I know nothing specific about them, but they have a devoted following here.
4) Bedding: For Shavings: Aspin is great. Pine or Ceder or any other aromatic bedding is horrible for their lungs. The lower 'dust' level to the bedding the better. Another favorite is "Yesterday's News" brand paper bedding. It's lower dust than others. Many people simply line their cages with cut to size fleece/flannel. You can get it in the scrap bins of fabric stores.
5) Space: They will need out of cage social time every day. At least an hour is ideal. Some people have a designated Rat Room. Others build a rat play pen. Some let them have free run of the house. The area (s) you allow them free time will need to be rat proofed and safe for them.
Here's a site with some suggestions on Rat Proofing: http://www.80stoysale.com/ratproof.html
6) Food: Here's a good link to get you started on your rat's nutritional needs: http://www.pxrats.com/ratfood.html
Other than reading through this forum, other good resources for you are:
This site covers everything from vet care to socialization and most things in between.
I have found Goosemoose forum to be a treasure trove of archived information. Specifically the "Rats Rule" section which has the Reference Desk, Rat Care, and Home Squeak Home. You don't even have to join the forum to find what you need there.
And, pics! We wanna see pics! We loves pics!