This is a really great thread on coaster brakes with some fantastic suggestions and good information. http://motorbicycling.com/f41/dont-l...kes-21094.html
I know some great builders who like them and some folks don't. But with out a doubt, you are gonna want front brakes. An emergency stop at 20 or 30 MPH can be hairy! On that thread there is a product I had not seen before. Sort of a horseshoe shaped thing that would work for you. Many options. Also, could see if your BMX fronts can be adapted. Folks do get by with coaster brakes alone, but I couldn't suggest that. If you do for a bit just try to look ahead and slow early.
Here is a search for front brakes and adaptations. front brakes - Google Search
Cool part of here is bopping around reading will answer questions you didn't have yet and give you some really cool ideas.
I can't wait to see your build done. That is an awesome bike.