They have 3 guys who have one year to play. The DT from arizona. The cb from arizona. And the de from Purdue. I guess you go for guys for one year if they can come in the spring and if they are at a position of desperate need.
I would think Dorian springer from arizona will be a one and done As well
Imo you really should try as you build the team to stretch this out and rely less on transfers or go for guys who have 2 and 3 years left. Using the transfer school as a jc for the kid to make grades. Beef up in weight room and get used to collegiate size and speed.
One and dones for wrs and rbs is probably ok. Just about any other position really needs to be 2 yrs minimum (yes there will be exceptions, like Haskins). OL, DL, QB, LBs, DBs really need time to gel together or learn the system and one and done is going to hurt your program eventually if this is done excessively at these position groups.
For OL especially this seems like a good plan: evaluate how the most difficult position to project plays at this level first. USC, as a blueblood, can get new, experienced OL every year. Preferably with 2 or 3 to play.
They appear to be doing it along the offensive line