Can I stud out a wall without removing the plaster
Freestanding steel studs are fine (assuming they are anchored to a sill and top plate). Steel studs anchored to the furring strips are fine. Why wouldn't steel studs anchored to the furring strips, plaster and lath be fine? The only limitation would be if the lath and plaster had significant bowing or hollowing in spots that the new studs came in contact with (minor hollowing would not make much difference).

Also, as you install, you want to make sure that crumbling plaster does not get wedged in a way that prevents the studs from creating a smooth planar surface.

While plaster is not much of an insulator, you still have a bit of air trapped between the plaster and the brick in the furring strip troughs. Add high density batts or rigid foam between the steel studs to improve the R value.

If you are very concerned about insulation, wood studs are poorer transmitters of heat and should be considered. Also, creating a real thermal break by not having the inner wall directly abutting the outer wall would improve the situation. But this approach does eat up interior space.