Hey--I just finished something really similar. I'm new to this so I went the easy way and just got an MIM Tele body loaded off eBay and stuck a Warmoth neck on it. It sounds great. My first build (which I will get to one of these days, I swear!) is going to be *exactly* what you're talking about--tele body, two p90's and a bari neck (still considering the varitone--not sure I'll use it).
I have a question for you though--How exactly do you plan to fit a p90 in a tele bridge? Are you just gonna get one for a humbucker and use a humbucker-sized p90? I figured w/ mine I was just gonna use either a strat-style fixed bridge or, if I can find one, a ASAT Special-style top-loader (thems some nice bridges, I'll tell you what).
Anyway, Baritone teles rule this world. I'm gonna go play mine right now. Keep us up on your progress, if you will.