A fuel filter will be a bit too fine, if you have an engine oil filter base that could be made to work, just be sure to mount it filter down / dirty oil to outer edge of filter / stick a magnet to the filter to capture steel bits.

You can get filters specifically made for trans cooler lines. Check the diameter of your hose and get a filter that has matching barbs. 8 mm / 5/16" and 10 mm / 3/8". Have a look here for inline filters Service-AT Inline transmission filters Shop around as while SPX Filtran is an excellent brand, these seem $.

As for shaft end play, generally if you don't replace "stack up" hard parts, the end play will be the same as when you started. It is still a good idea to check it.

For adjusting clutch clearance, trans use different thickness snap rings , pressure plate ( the first all steel plate that is installed in the clutch drum. ) intermediate steel plates and rarely friction plates. There is a generous range of clearance and sometimes what the factory says to use doesn't work so well in the field.