Considering how large it is, my first choice would be to sell it for something that fits. If the bicycle fits, you'll enjoy it more and ride it more often.

The squeaky rear derailleur is a simple repair. The pulleys need to be removed, cleaned and lubricated. Wobbly cranks could be due to loose or worn bearings, loose crankarms and/or a out-of-true chainrings. I'd attmpt to fix these issues. It will bring more money if you decide to sell it and even you decide on S/S, you'll at least need to adress the crank issue.

Regardless of what you decide to do, I'd appreciate the serial number for my database. TIA.