I have dryhopped with 0.5-1oz in 5g, so I would say 0.25-0.5oz would be good for 2.5g. David's experiment sounds interesting...dry hop with a different variety in each secondary. Or dry hop with one variety, but in varying amounts.
I've always just heaved the hops in...never sterilized, never had any problems from hops. Leafs will float and pellets will sink...either way they can be avoided when you rack for bottling. With leaf hops I'll affix a sterilized hop bag around my racking cane to keep 'em out.