I'm not a carpeting grower so I'll skip that but comment on question two.
I advise caution here as there are so many myths and half understood "truths". I don't see any need or reasoning for that much filter.
I consider what a filter is designed to do for me. One is mechanical filtering to get the water clean looking, two is bio filtering to process ammonia down to nitrate, The third is chemical filtering which I pass on as unneeded.
If my current filter was not doing it's job on any of those, I would feel I needed more/better filtering. But most of the time we see people adding more filtering just because somewhere they have read a magic number of times the water needs to pass through the filter. I see no logic in water passing through a pint of media twice is any better than passing through two pints one time.
If the filter is working fine and keeping up, there is still one other reason people add filters. They want more circulation in the tank. For this , I find it much cheaper and easier to deal with simple powerheads rather than expensive, maintenance heavy, filters which are hard to aim into the correct spots.
If there is a need for filtering, add filters but not just because of "magic numbers" that you read about.