The connectors you have there are MFM/RLL interface connectors for (very old) hard drives. The A2090 controller you have was made to primarely support these drives. It does have a SCSI port but is really isn't of much use.
If you want to fit her up with SCSI hard drives and a CD-Rom drive you will need another type of controller. An A2091 would be a good bet.
The memory expansion is
THIS ONE. It looks like it is populated to the full 8MB, thing you should keep in mind when going for a SCSI controller: take one without any extra RAM as your A2000 has as much ram as it can handle, apart from adding a accelerator board.
The cable you see there looks more like a fuse to me, and the fact that the two cables are soldered both very close to an external connector would make sense. Probably a fuse was blown on that port, and the previous owner replaced it with a rather large one!
And you have a so called Flicker Fixer! Nice, this means you can connect a standard PC VGA monitor.
