I’ve always had good results with the superstar rear sprockets.
Chain of choice is the KMC Z610
As for tensioners you have options:
Of the sprung type I liked the surly one but it was expensive. I replaced it with the on-on variant when I broke it* and that worked well. I never found it particularly good in push up mode (I had different springs for the surly).
Never used a fixed one. *In principle they should be more secure stronger and seem to be more tucked away making them less likely to damage. I was always worried about getting the wheel out and the faff in having to loosen it off.
For stuff I would look at the following shops
superstarcomponents
velosolo
charliethebikemonger
on-one
CRC