PInky Fizz Bum,
I am not a parent, nor know anything about autism etc, but what you are saying sounds like normal behaviour.
His thing for numbers, is it any different for a childs obsession with football or rugby?? They have their bedroom decorated the teams colours, only wear the teams football shirt, collect stickers, memorabilia, etc etc.
I do not know how old he is, but when I was about 6 I become obsessed with dogs. I read all about them, wore doggy T shirts, visited rescue homes and played with them for hours. The only danger, my parents forsaw was I could not resist stroking ANY dog in public. Luckily I was never bitten.
I think numbers and sciencey things is formed in a different part of the brain to the artistic side. If he flourishes in this, then I am afraid the only bad thing for a parent is he will probably grow up a boffin, earn �500K a year and get married to a girl called Clarissa from Surrey.