Everything I read on trimming a stair case (in oak) they all install the riser first, then the tread. The only reason I can think of for doing this is if you ever need to replace the tread. Is there any other reason?

I ask this because out basement stringers were framed with 9" run and 7 1/2" rise. Most I see have a 10" run. If I use the pre-fabbed oak treads with a return they will hang out too far unless I install them first and the riser second.

I guess I can always re-cut the stringers.

Yea standard steps tread stringer are around 7 1/2 rise and 10" run, give or take alittle
as for the risers, we do install them first, its easier to make tighter joints, as for another reason other than thats just what we do i guess,
as for puttin on the treads first i dont see a problem with that if it is in a basement where the joints dont have to be all that tight, but if you want them tight youll be doing a lot of scribing and planning to fit them,
in your case i think id just add to the fronts of the stringers , just an 1" put the risers on first then the treads