in the UK electric bikes are legally limited to 14mph; don't bother converting an existing bike. £1000+ will get something good, the cheap ones are over weight dogs.
P.S. if you don't mind pedalling then why not just buy a bike, it's a sight 'greener' than a bike containing heavy metal based...
I wouldn't, it's a race bike designed for racing, not freestyle. They are 2 different things and the design differences are subtle but definite. Race BMXs simply aren't designed for the abuse/hard life of a freestyle BMX.
"is there anything around that price range that doesn't totally suck?"
NO!
If that is your top budget then look for something as simple as possible, the less gears, disc brakes and suspension a bike has then the better quality it'll be...
your legs say 19" but your height says 17". The 19" may be a bit of a stretch in the top tube length, but running a 17" will mean a lot of seatpost out, a tough one to call. You realy do need to 'try before you buy' or at least sit on them. Did yyou measure your inside leg without shoes on...
I don't know that concern is the right attitude, it's meant to be fun. Take it easy to begin with and don't expect to do 30 miles on your first trip. Wear a helmet, take it easy and enjoy.
E-bay for old parts and accessories. If the rust is on chrome try 'autosol' or any other chrome polish. If the rust is elsewhere (frame etc) then short of touch uppaint or a full respray there is little you can do other than paint 'rust inhibitor' onto the affected areas, that'll stop it getting...