Is the 2005 crf250 a good dirtbike? Or Should I try and buy newer? Is buying a 4 stroke risky?

Sounds a little iffy. The 2005's are a bit unreliable how they are, I don't think one with a larger bore and unadjusted valves sounds too good. I would try go for a 2007 - 2008. 2005 wasn't a really good year for 250F's. They didn't really get good until 2007.