The additional wires off the fusebox are not factory and are where an installer (dealer or otherwise) of some aftermarket piece of equipment (radio, alarm etc, lights) selected to take power from. This assumes that they are not replacement wires for the originals which failed at some point. Fuse 2 is for interior lighting and power to fog lights/relay, fuse 5 is for the left of right turn signal. See if you can trace where they go.
Is the buzzing coming from what appears to be an under-dash relay? These cars have an incredible annoying open-door indicating buzzer. Under the hood I am not sure, but it may be a normal function of the Si's injection system (ie an idle valve or something like that).
Your bouncing tachometer indicates that the tach is getting an electrical signal from somewhere. Unplug its signal wire at the ignition coil and see if it stops. Perhaps your ignition system needs to be sorted or adjusted, and there is some sort of short sending a signal to the tach with engine off.
I am not sure what the large relay is above the wiper interval, likely something found only in the Si models. I am sure someone can help you out with that one. The other dangling unit with the knob is a speaker balance/fader unit--you can see the speaker wires attached to it.
Those three lose, hanging wires on the left of the column may be unused from the factory. Not certain on this, but I think that they may be for a factory fog light installation or the like. Pretty sure my Bavaria has them hanging as well. I would leave them alone for now or someone else might have an idea.
Post some pictures of the rest of the car so we can see what you are working with! Paint under the fusebox looks like it may be a Turkis colorcode? You'll get there. My Bav was off the road for over 30 years when I purchased, now it is a daily driver in the summer months.