Re: First build in progress!
Nice looking 1st build so far.
You like that 'get low and sleek' setup I see. I am more 'sit straight up' kinda guy but you build to how to you want to ride, which is part of the beauty of building your own bike.
Just a couple of things that may help.
You can get a pair of side-pull brakes with cables and levers for under $20 on-line, heck even less at Wally World. They have one mounting point, right where your fenders mount and have their own bolt to hold both the brake and fender on.
Pop a SickBikes dual pull lever on the right side and instant self-adjusting brakes with one lever, then just use the coaster brake as a back-up.
Pop of the typically 18 tooth sprocket from the pedal side hub and put on a 19 or 20 and magically your coaster brake works great and your bike gets much easier to start.
*Note that with the lowering gearing you will need t mess with the pedal chain again, and when pedaling only it won't go as fast, but it will still get you there.
As for the coaster brake arm, it doesn't have to fasten to the lower chain stay, they quite happy attached to the upper frame bar and don't need some massive bracket to keep them from rotating, just any 'ole metal strap, bolt and nut will do it.
I find it best to try to get the drive chain sized with the wheel as far forward as practical with a new chain and of course no tensioner.
Once you get your initial sprocket and chain wear out of the way you can just move the wheel back to tighten it back up.
That in mind, leave a little slack in the pedal chain. It will not wear or need adjusting near as much.
If you need a little tensioner no problem on the pedal side no biggie.
Without having to reply on the coaster brake you may not even need one at all.
Every bike I have built has had a black Grubee SKyhawk.
No issues with any of them, not even heat, and I am in the desert (it was 109F today).
Hope those help.