If you move the bottom mount inboard you increase the chance of bending a wishbone if you say hit a pot hole. the spring platform is the bit the bottom of the spring sits on, zimmers have large nuts on to adjust this, compress the spring more the ride hight goes up but you may get to the position the spring goes coil bound under normal use.
For spring compressors you will need motorbike ones, NORMAL car ones wont fit.