As far as doing AmigaOS 3.9 it looks like I'd need either a PCMCIA->SCSI plus SCSI CD-ROM (which if I dig deep enough in a closet I might still have) or do the Rapid Road USB (that connects to the clockport on an A1200?) along with the fancy 2x backplate connector. I've already got the external USB CD-ROM so that part would be covered. After that in theory I'd be able to read a CD-ROM and thus be able to install AmigaOS 3.9... yes?
The ACA1221EC has a clockport which is supposed to provide better speed than the one on the A1200 although I haven't seen any benchmarks. On the standard clockport with a 68030 @50Mhz it achieves around 700KB/s, on A2000 with 68040 @33Mhz it 1.5-2.1MB/s and on an A4000 with 68040 @40Mhz around 6MB/s.
The CD drive should work with Poseiden. Reading from another thread you may need to mount the drive manually in the OS.
Another option some people use is to hack a laptop drive into the A1200 case and connect it via the internal IDE port using an IDE splitter. It probably makes more sense to get the Rapid Road since it's you can connect different USB hardware. You may even be able to install 3.9 from ISO image on a USB stick.
I think some people install the OS on CF or hard drive using WinUAE on a PC.
