I'm down with numbers, too. I'm not sure if this could be considered a hobby, but I count everything. Any time I am doing something repetitive, like walking or brushing my teeth, I'm counting the number of steps or brushes. Usually it starts out subconsciously and then I'll realize I've been counting for a while.
I've also recently been learning calculus just for the hell of it. It seems like it could come in handy one day, especially if I decide to go back to college.
I wouldn't consider counting to be a hobby really... but learning about numbers? Calculus? Stuff like that? Definitely!!!! It's addictive. It's fascinating. It's really a basic building block of reality and understanding the universe that surrounds us.
Other things I've done with numbers include: working at the IRS, designing much of an airplane (on paper), taking accounting classes for fun. It becomes a hobby once you give up worrying about what people think and say f*** it! I like this stuff! A gf walks in, sees a 3-figure drawing of an airplane and says, "Oh, my son could draw something like that." and you think to yourself, "Oh, you have no idea how many hours of calculations went into that. I have a binder full of them!"
And the funny thing is, I'm not really all that OCD to be honest. I'm actually not a very neat or orderly person at all. I'm a "scattered thinker" who's struggled enough in school to have been forced to learn some amount of order just to get through... so now I use that when necessary. I use order to make sense of all my crazy numbers. My football spreadsheet has literally thousands of cells to it. But if anyone else looked at it, it'd be a jumbled mess. But it has enough order in it for me to make it work for me. As contrasted to my "natural state", I'm actually surprisingly capable of keeping things orderly... I just don't often see the point.
But numbers-stuff are things I keep coming back to. When I was in law school, I strangely gravitated towards Tax Law after studying aircraft maintenance for 4 years. When I was a kid, I was crazy about keeping track of baseball cards by their numbers. I would calculate percentages. And as I said, this wasn't my first crack at a football betting system. I did it many years ago. I also worked out and tested Blackjack systems before deciding that even the best of them wasn't enough of a sure thing for my liking... yeah. I'm not a fan of gambling really. Oh, and of course the stock market. Back when I had a good job and some investments, I was doing very well for myself. But, alas, no spare money these days. Can't even afford to get my car fixed. Ah well. Maybe this NFL betting thing will pan out. lol