Now, which of the three options should I get first? (CD ROM, Printer, Networking)
Networking, printer (close second), cd-rom (distant third). In that order.
I often use networking with my Miggies (3C589), quite often I use my printer (HP 4L) and hardly ever use my (scsi) cd-rom and/or (scsi) cdrw drives.
Tip: if you mostly print in black (and white), think about buying a good second hand laser printer. They cost next to nothing, print 1000s of pages per toner cartridge and don't suffer from dried up ink cartridges.
Although many people in this thread are pro-ide, I prefer scsi. It gives you more expansion possibilities and goes for a neater solution without flat cables running around your desk. Downside is, that hardware is more expensive.
My current scsi-config is a 4-drive scsi tower with hard drive (18 GB), cd-rom, cdrw and 100 MB zipdrive and two single drivecases with a Syquest 270 MB drive and a 230 MB MO-drive, all connected to a Blizzard scsi adapter. Looks nice, works perfectly.