1. If it has a 1.44mb drive and appropriate swim, eg the FDHD did.

2. "PC Exchange", later versions of System 7.5 had this built in.

3. When you try and format a disk what capacity does it say? 400kb, 800kb or 1.44mb, or does it just say single-sided/double-sided?

The Classic has more surface mount components, 32 bit clean ROM, smaller motherboard, insane memory expansion.

The SE has a slot that can be most usefully filled with an ethernet card.

I recommend putting 4Mb in the beast.