elight,
I am NO expert, but I think your setup looks pretty good. It should work fine. I built a dozen tainers recently based on Raybo's plans. Used that exact mini float. Using a hose hookup though, not a gravity feed.
Went with 3/8 in sizing on everything to keep it simple and because I will have a fairly long run from the spigot. Otherwise I think I would have used 1/4 in across the board.
1/4 in ought to serve your purpose well.
I went with T fittings as well as opposed to a Daisy chain. Thought process was it will be easier to take a tainer "out of service" if I need to. That and didn't want any possible "contamination" issues from one to next. Don't know if that is a real concern or not. I will have 2 tainers of peas, and at least 1 of carrots in addition to tomatoes though, so the fertilizers will be different.
Haven't water tested my system yet. Pressure test is slated for this weekend. Peas are in potting blocks in my basement and need to get in their new home asap!
Suppliers -
Valves -
http://www.thevalveshop.com/menu/man...k/kerickm.html
PE Tubing (black) and fittings (went with Parker liquifit) from here.
https://www.freshwatersystems.com/c-...-fittings.aspx