Sounds like you have a good plan. If you do want to add a center pivot front brake, I’d go with the old DC Nippon. Those seemed to work pretty good for what they were BITD. More importantly, put some good brake pads on it. 😁
You might be in a slightly different boat to me but here's my street/flat setup (more street because it is a little beefy, but it does the trick)http://www.global-flat.com/smf/index.php?topic=66705There are a few tweaks now, swapped out the Odyssey R15 for the F25 fork (front brake mounts) and at 20" it fits well for street with me also being about 5'7". Apart from the longer rear end and fat tyres it's very similar in feel to the 'pure flat' setup, just more comfortable to chuck around.http://www.global-flat.com/smf/index.php?topic=67157I think you'd probably find a decent 20"tt complete would fit the bill just fine, swap out anything that breaks for lighter/stronger/cooler as you go, and don't feel too precious about scratching it!