"99% road. Can 100mm come off seat height and still keep good handling?"

You'll need a new fork spring and a revalve, as it will move around too much on the road. You'll also need a new shock spring and a revalve and then it will be pretty much a dedicated road bike. The exact amount it can be lowered depends upon the amount of travel you still have and where the rear suspension starts to become firm. So as you can see a bit of set-up required so we would need the bike in the shop for 2-3 days to get things worked out.

Front:

• Lowering, Fork Revalve, Service Set-up and spring

Rear:

• Lowering, Shock Revalve Service and set-up  and spring