I too am curious to see if that fuel line set up works. That said, I can think of a reason why it wouldn't....but enough suction to get it primed could be an issue. You might need primer bulbs prior to the T. Keep us posted.
I am actually in the middle of converting two 6 gallon tanks to a single 14 gallon aluminum tank. I LOVED being able to run off of one tank until empty, then switch over to a full one. (This was an easy way to know how much fuel I had left.) So, I would recommend a switch (especially if your set up doesn't work.) That said, the switch does add complexity to the system. The previous owner of my boat had primer bulbs for each line prior to switch and it seemed as if it was needed for my setup.
I started having fuel delivery issues and I could never really trace it down to 100% certainty to what the problem was. I switched lines, tanks, switch positions, new fuel line, etc. Ultimately, I think it was one of my ancient fuel tanks. So, decided to pull it all out and install a new tank. Will wire up fuel gauge in dash, etc.
Your project looks great man! Good job. I am dying to move up from a 16ft to something larger.
KRS