The service manual is the best you're going to get. Like most macs they never really had an owners manual. Just a quickstart booklet which told you how to plug peripherals in and the OS users manual which generally isn't machine specific. If you aren't intentionally going to need a fast SCSI bus you can get away with using an old 4 or 9gb SCA scsi disk (they're pretty cheap and easy to find these days) with an 80 to 50pin adapter which will max out the bus and for the most part won't be annoyingly slow. NuBus SCSI cards have a reputation for being quite expensive.