Ryanair have 9 based, with I believe 10 in the summer peak.
Flybe have 8 based and as you say, use many away based flights such as Loganair.
In terms of overnight stands at T3:
Ryanair have 9/10
Flybe have 8
KLM/Air France have 2 night stoppers
BA can have up to 3 (1 A320 and 2 E190 at weekends)
There are 20 stands overnight with some Flybe being remote parked at the moment.
One would assume BA/AF/KL will move over to T2 once done so that's 3 stands freed up. T3 certainly needs more bussing hates if Ryanair were to expand based aircraft further, but of course, Ryanair do bulk out their schedules with many away based flights.