Hi Although i am not removing the subframe I have been dismantling the passenger side hub and lateral links. Mine is a 2000 model.
As a matter of course i replace the bolts as i go. Subaru recommends at least changing the nuts("lock nuts"). Watch videos of Mr Subaru on Youtube and the others before you start.
Here is a link to the manuals for JDM cars Index of /Auto/Japan/Subaru/Impreza (jdmfsm.info).
You should be able to pick up the torques required and info about doing the job.
One job your going to come across is removing the bolt holding the lateral links to the rear hubs. Its a long bolt and takes some persuasion to come out.
If you need to replace bolts on suspension they generally are not metric course threads, but fine or super fine + high tensile. Not sort of bolts you can pick easily. Even from a engineering bolt supplier. If you need to remove the brake caliper from the back plate, buy new bolts. These have a habit of rounding the head off.
Both links below are sources of info i use regularly, ICP are particular good. Lots of Impreza parts are the same across various models, including Foresters, Legacy's etc.
I also use Autodoc GmBH for some parts. If you need to rep[lace shockers they are probably KYB, their catalogue is online for coils and shockers.
My new rear drum/discs are marked for a Legacy.
