Pool Water level for closing

I closed my fiberglass pool here in MN today, I think I did at least :)

I left the water at mid skimmer level, but have it block with a leak proof thingy a majig that I bought at the pool store. I used a gizmo, duck plugs, and an air compressor connected to the filter pump's drain plug opening.

Three questions:

1. My fiberglass pool has tile at the top and the water is about 1-2 inches up it, do I have to lower the water to protect the tile? I have an autocover and don't want the water to low. Plus I am in clay and prefer as much water as possible in the pool

2. I have 2 main drains in the deep end of the diving pool, 8-9 feet deep, on the bottom of the wall (not the floor) about 6 feet apart. They are connected by a junction about 1-2 feet behind the pool wall. ( saw it at install this summer). I got great bubbles of air solid and good from the main drain nearest to the equipment pad. I suspect this is because the air was taking the shortest path out to the pool and possibly the least resistance. But NO air came out fo the further away main drain at all. Even dove in to feel any movement none?
As they are joined by a T how do I get air over to there or do I not have to worry as it is 9 feet underground?

3. I had them install perforated pvc in rock base with fabric between layers and a pvc pipe that come to the pool deck, at the deep end of the pool. Do you do anything with this over the winter. Should I put a shop vac down the pipe and see if anything comes up? Put antifreeze in it?

Thanks for all the help, we live in Minnesota for clarification

Tasso