If I was going to put casters on my freezer I would build a wooden platform with the casters on it and place the freezer on top. Does not look like enough good support for the casters on mine. If you lay it on the side, you need to give it time to recover before turning the unit on. I don't know what the official time is but give it a day to be safe.
As for collar, I went with a tower so I can't help. Start up tips = make sure you have correct beer line length depending on your temps and serving pressure. Many posts talk about that.