If he's older, and by older I mean starting to reach senior discount age for a rat, I wouldn't bother with a friend for him. Being alone his whole life he may not take kindly to one. It's esier to intro adult females to eachother than adult males though with that said I have NEVER once had trouble adding new rats to my existing colony. Though it is nice to keep a furry friend in with a hairless I've always heard. I had two hairless females but they were only two out of 10 if you get the general idea lol. You don't have to have males neutered for any reason, and you can intro intact males to eachother and keep them happy. I always had my boys done to reduce the smell and urine marking, which only my intact boys have ever had a problem with. You CANNOT introduce a female for obvious reasons. Single rats that have been happily single for a long time are usualy ok remaining single so don't sweat it. Obviously they are best kept in groups but being a rescue you might not have had that option. Any new rat comming into your home has to be quarenteed for at leaast 14 days. In order to do this properly you really need to keep them somwhere with a completely seperate air supply. It's as much for your current rats protection as for the new one.
Food, it;s harder to find real rat food than you might think. "hey look walmart sells some..." Nope leave that on the shelf unless it the little cubes from 8 in 1 that they sometimes carry. Thats not a terrible food. What you really want, and you're lucky enough to be able to get easily here in the states, is something like Mazuri rat food. Mazuri is a purnia company btw. They sell it at alot of petstores now, petsmart jumps to mind. The other thing I fed my rats for years was the senior forumal nutro natual choice, in the brown bag. You're looking for lower protien than a dog would need. I supplemented with fresh or frozen (and then thawed) veggies, usualy the mixed kind with peas, carrots, green beans... you know the stuff. Apples are nice and I learned never ever to get between a rat and his strawberry LoL.
The Aspen is fine for bedding, I never did care for the paper stuff personaly except perhaps yesterday's news. It was the only one. Pine and cedar are no no's.
Cage; wire is best because it allows for good air circulation which helps since small furries can be so prone to respitory illness. The bigger the better I wouldn't consider keeping a rat in one less than the size of at lest a 20 gallon aquarium. Thats just a size reff. for you, wire is still a better bet. Shelves to maximize space are also great. There is the arguement that an aquarium would help retain heat which might be important for a single hairless but in my experience it's not needed. Just provide a good house and some blankets or a hammock in addition to bedding for them to cuddle in.
Sure wish geocities hadn't closed, it deleted my entire rat website, had a HUGE rat care guide on it with photos and everything. With wire cages it's nice to cover the cage floor with something solid (not wood) to avoid food injuries if the cage has a wire floor. I used cheap-o fleece blankets, and sometime carpet samples. There are tons of ideas out there though if you google the subject
here's a picture of my big cage to give you an idea, (fleece was in the dryer after being washed in this photo)
this is my big cage, it's 3 feet by 3 feet (would you believe I only paid like 100 bucks for it brand new and that included shipping?!?!) it' housed up to five rats at a time usualy my max number that I keep.
