I've been able to use several SCSI 1 drives on my classic Macs. You should be able to reformat any drive with the System, Apple's drive setup tools, or third part programs if you have any. I've used anubis drive tools on my old hard drives on my Plus and SE and I swear it could even resurrect old harddrives and make them usable for my old Macs.
The easiest thing may be to get an Apple Utilities / Tools floppy image from Apple, then write it to a floppy using something that can write floppy images. After you do that you should be able to boot from it and format your new hard drive.
As far as downloading things off the internet, if you have Ethernet in your Mac it make things easier. You can then use a web browser or a tool to save files from a URL.
Good Luck!