Re: Skyhawk Frame up build
seat post size is 27.2mm, id recommend chopshopcustomz he makes really good quality solid steel seat posts and you can have it designed whichever way you would like!
Why run a derailleur? Are you planning on running a shift kit or a jackshaft kit? If not id suggest replacing rear wheel with a HD coaster wheel. The standard size hub-sprocket adapter fits any standard coaster wheel, makes life a lot easier, also it adds an "emergency brake" if things get crazy hehe
Look at the fuel shut off valves from SickBikeParts. I have one and am very happy with the quality, although im sure you can grab one from your local hardware store and have it work just the same.
The bottom bracket is a standard size, 2" i believe. I reccomend running a BMX 3-piece bottom bracket, they have nice sealed bearings
Performance twist throttle from sickbikeparts, they have a nice roller bearing pulley system
Thats all ive got for now! good luck!