Lovely looking bike! SS MTBs always look so purposeful.
White Industries ENO are considered pretty much the best freewheels. Not cheap though.
Are you already on 32:22? It will be pretty spinny on the trails with 27.5 unless you live somewhere super hilly. I used 32:20 on a 29er for the North Downs and that felt about right for that kind of terrain. But obv use whatever feels right for you!