thanks for the comment FishFriend1, did a little bit today. Sand and protective layer is in.
Tomorrow it will be pumping out some of the water and then straighten out the liner, roll it out to the other side and silicone the bottom-drain in I hope.
Wait till Thursday and then test-fill it. Will also have the 2nd Dome painted tomorrow, so Friday that one can go in.
If the first test fill goes well, then slowly further fill it and wait.
All works out, then saturday finish filling at 70-80% and also silicone the skimmer in.
Connect that one to the settling-tank and have it all drying before starting to look at realistic schedules for switching on pumps and let it run for a while for testing.