Hi Ron,
Have a look at Woosh, all plug and play kits and good customer service, UK supplied.
You can go the route of individual components but you have to be prepared to get the soldering iron out.
I think front hub is the simplest for first installation. So long as your forks have a 100mm drop out, there shouldn't be any major problems. Rear hub, you have to take note of having either cassette or freewheel, and buy the appropiate motor. Dropouts are generally 135mm sometimes chainstays have to be sprung slightly.
Front hub and bottle or rack battery distributes the weight. Rear hub with rack battery is quite tail heavy, frame battery better.
Fitting the pas magnet and sensor can be the trickiest bit (depends on the bike) but usually nothing that a bit of good old in the shed inginuity can't sort out.
Best show us the bike you have, the type of riding you want to do, then we can help more specifically.