Hi. I have some suggestions.
Type of Filter.
I would recommend the Fluval. 304 or 404. others may suggest otherwise but I have both and both have been running for the past 5 years.
Changing Media.
Not too often I have only ever washed my canister filter once every year,
Ease of use.
Very simple to do and clean as well.
You will not need to change the medium unless the sponges are completely full and falling apart (once a year), Carbon will need to be changed if you do use it (once every 3 months). apart from that there is nothing to change
Use of Airstone.
Not necessary if you place the spray bar above the water line (problem is that it can get quite noisey)
Continue use of UG Filter
Yes untill bacteria is built up in the canister filter.