hi :)
Winuae is the best emulator:
Winuae. You don't need any other emulator.
For the second question: install a hard disk and a cd-rom drive in your 1200. That way, you will have access to big collections of demos (aminet cd's or scene archives for example). For 3.5 inch disks, well every dms can unpack to disk but most A1200 demos from after 1995 should really be installed on harddisk anyway (too much disks).
Hope this helps.