Hi, if you change the freewheel you will need the right tool, plus I found I was only able to get the old one off by putting the tool on, flipping the nut (the built in washer means you can't get the thread to grip, tighten the nut a little to hold it all in place and put the tool and wheel into a vice on a workbench, then turn the wheel to crack it to start undoing it, hope that makes sense. I also got a bit of oil worked into the freewheel in the ports on the reverse before fitting it.
I still have the same chainring/chainset on. that said I do like some you can get that look cool, but would want to be sure I don't change the chainline on the bike so not touching it at this stage.
I also did not mention I changed the bottom bracket which also started to go after I had been using it for a while. After a bit of research I settled on the Genetic Karyotype JIS bottom bracket. Found a good seller of them on ebay, around £30-35. just need to make sure you get the right size, 68x103 for this bike. https://www.ebay.co.uk/itm/Genetic-Karyotype-JIS-bottom-bracket/112754983789?ssPageName=STRK%3AMEBIDX%3AIT&var=414403045242&_trksid=p2060353.m1438.l2649
this is a good crank extractor for this, I had an old crappy one and bought this its very good, just make sure you have the threads seated nicely:
Park Tool Cotterless Crank Puller
and would need the bottom bracket tool as well.
one last point, although the schwalbe 28mm tyres do seem pretty bomb proof I do always carry a 15mm Spanner just in case I needed to take the rear wheel off if I got a puncture. I do get the occasional sarcastic remark when I was riding with others (when it was allowed anyway!), about my spanner in me back pocket :-)