Can a septic system leach field be installed over clean fill?
I have built on filled areas in the past, you have asked all the right questions the first being compaction. In the area I built we had added 4-6' where the house ended up and closer to 8' closer to the back half of a drain field we filled and compacted and met the code back then but we're still required to wait 1 year and repeat the 3rd party compaction test. After that perculation testing after we had 50% of our normal annual rain fall took 2 more years because of a drought. But then we were able to get permits to build. If you are going to be waiting a few more years you may not need the additional compaction testing it was a bit expensive but turning a worthless lot into one worth 80k for just the land it was a no brainer for us.
You have the soil to move around but you would be amazed how many quality loads of fill dirt can be had for a couple of cases of beer. May not be quite the same as this was many years ago at the start of mound systems and they cost up to 10x of a standard field plus the maintaince. But your plan sounds good to me.