I have ML SL3's, and previously used a HSU 12V with reasonably satisfying results. Be careful of it's placement as it can sound bloated, particularly when using something like an electrostatic.
Regarding main speaker placement, ML suggests 4 ft. from wall, which is where I have them, with Auralex panels behind to minimize reflections from the hard wall. If you have to go less, you'll have to deal with rear reflections to make them sound good. Too close to a back wall can make them glare at higher volumes. Auralex panels can do wonders (www.auralex.com) in making them sound good.
Room size is dependent on the model. I have Aerius i's which used to be in the front but are now in back that functioned well in a room half the size.
I'm using a Bryston 4BST (250wpc), in a fairly good sized room (25x30), and wouldn't want much less. I'd say 150 is absolute min., but again, the size of yuir room will dictate power requirements.