I’ve built an OSSC 1.5 for myself and a few OSSC 1.6 for others in the past using just a decent soldering station, a multimeter and a cheap head mounted magnifier. You don’t need a lot more than those tools. My first one (the 1.5) had some problems as well because of some shorted pins on the U1 and a faulty capacitor. It took me some time, but i figured it out… and now it works flawlessly.
I just recently bought a microscope since i have to solder more and more fine pitch stuff for hobby repairs. It comes in handy for checking solder joints but it’s not needed by any means to build an OSSC.