First choice is cedar trees followed by xmas trees. Willows will be gone in a few weeks due to Beavers. I have caught thousands from suspended xmas trees.

Forget about the treatment idea. I've never found it to be an issue.

The light may help after you put in the trees but is not necessary.

I have cedar trees, willows, empty bucket tree and pvc trees in mine and about to put more cedars in this weekend. I dont thing you have enough water under your slip for winter time fishing. I might be wrong but I have 24 feet of water under my boat now and the fish in the winter seam to hold about 18to20 feet. They will move up in the spring.