New set up, need advice

[hillegom]

Yes 3 days is good. Some people change them every week.
Some people can't be bothered.
Filter socks collect detrius among other solids, and copeopods too. If you don't collect the solids, then they will pile up somewhere and decompose "rot".
If you collect and take them out of the system, then you are doing a nutrient export kind of thing. Less nitrates your system has to handle, less water changes IMHO
All depends on your bioload, how many fish/corals/food you have in your soon to be system.