I'd start with the following:
- Inspect your work on reassembling the keyboard for any stuck keys, also check that connectors are tight, etc.
- Run a floppy drive head cleaner in your drive a few times
- Try booting with a different copy of Workbench disk, if possible
I would check keyboard is put back together properly - you've not let water get in there have you? ie after retrobrite you dried the keys, put spring under each key etc? If you are testing with key caps off it will think you are pressing some of them.
Regards the floppy errors it sounds like the disk detect sensor is playing up. Theres a pin switch that presses when the disk is it the drive, sometimes those switches need cleaning. Also, the spring that pulls the mechanism closed when the disk is in sometimes weakens which makes it not pull the disk down onto the aforementioned switch. Take drive lid off and see how it things are while its running - make sure disk mechanism is pulling disk down onto that switch.
I would clean the switches with WD40, but dont get it on the heads.
