I've had my Dwarf hamster for 2 days, and i have some questions?

Okay so Hudini is a Dwarf Hamster and my friend kinda gave me no other choice but to take him. long story short, she wasnt allowed a hamster, but nether am i so im hiding him. since i've had him, hes been living in a small hideable box, with food water, shredded toilet paper and a a toilet paper roll to play with. I looked up what i could feed him other than hamster pellet stuff and it said cauliflower so i gave him some of that. she got him on wednesday, with nothing more than alittle bit of food, and gave him to me thursday. I read that Dwarf hamsters usually need to be with at least one other of its own litter (brothers/sisters). I know that the place she got him still has some of the hamsters left from his litter and i was wondering if it would be okay for me to get him a brother today, along with some treats, and a running wheel and some things to chew on. And right now he seems to be getting angry and restless, which is why im going to get him stuff today. i am also going to look for a small cage, cause like i am not allowed a hamster.