Mechanical boost guages work fine. Mine's a $30 EBay SPW gauge, reads boost pretty ok (though I ahve no comparison otherwise).
As far as the MBC goes, I strongly suggest just purchasing an MBC instead of making your own. You wouldnt want your MBC to fail and become wide open.
MBCs are cheap as nails. Forget the TurboXS ones and the other "dual" types. I got mine from joePMBC.com for $40 shipped with all hardware for install already included. There are tons and tons of good reviews on his MBCs. It's worth it spending the slightly extra dough and just getting something that has already been tried and tested very successfully, than even having a hint of suspision (lo, sp?) on the home-made one. A bad MBC can blow the turbo if it decides to open on you. This is not to say that you can't make one yourself, but with such low prices, why not just buy it? Sorry, that did little to answer you question, but that's my two cents
