You can of course turn the Amiga off when swapping the drive
I've done hotswapping occasionally with SCSI HD on Amiga, but it might not be advisable. Bus rescan is needed with unitcontrol for example to get hotplugged HD shown. But don't try anything like that with IDE at least
For network transfer speeds... with 68k Amiga you can get in optimal config around 1MB/s roughly. With PCI cards. With Zorro cards you probably end up with 600kB/s or like that. With 060.. with 030 don't expect more than 300kB/s
So you can count times yourself.
