1. It can, but much better to connect it to the IDE interface.
2. No. You can only use one PCMCIA device at a time. IIRC there are PCMCIA "splitters", but they don't work on the Amiga AFAIK.
3. Any IDE drive will do.
4. Yes. You put the HDD in a PC, configure UAE to use it, install Workbench, then put the drive back in the Amiga. There are a few posts on this forum with more details which you can find by searching.
--
moto