as to your hard drive:
Remember, for a Mac Plus the drive has to be formatted using "interleaving" in a 3:1 ratio. Otherwise the Plus will not be able to use it.
The original Mac SE still used 2:1 interleaving, only on later machines the interleaving was 1:1 and thus the interleaving topic itself faded away.
Of course you need formatting software that offer you the option to select an interleave ratio other than 1:1. Presumably, Apple's HD SC Setup (included on system floppies of 68k Macs) will do.