I made my own cover out of a piece of 9mm Lexan using a micro CNC and covered the top with Kapton tape to keep out the UV light. The only problem is that there is no way to secure the cover. Other printers have tapped holes in the vat so you can just secure the cover with screws. It would be easy to tap the existing holes without interfering with the vat placement on the printer, so that is an option.
Even though I haven’t had an issue, I wouldn’t recommend leaving resin sitting in the vat for long periods. The solids will settle. I think the best practice is to filter into a vessel for storage. I would however, not filter back into the original bottle. I always filter used resin into a separate container and then add “clean” resin for the manufacturer bottle as needed for my next print run.
Vigorously shaking your resin bottle before dispense is a must in my opinion, then let it sit in the vat for at least 30 minutes to let any bubbles disperse. Homing the build plate, then moving it up 10mm or so and homing again will “mix” the resin in the vat. I have found this helps with print uniformity.