Front wheel drive questions

Hello – I am trying think of a way to mount a motor to a bike to use only on hills, so I can pedal the rest of the time (if I choose to). I’d like the powered wheel to be able to freewheel with as little drag as possible when the motor is off. What I’m thinking about is mounting a motor over the front wheel and replacing the front wheel with a rear wheel/cassette or maybe an internally geared one. But that raises a few questions: can the front fork be safely widened the inch or so it takes to accommodate a rear wheel? If so, what is the best way to do that? If I use an engine from a Chinese kit, I’ll have to jerry up some way to get the power to the right side of the wheel while still turning in the right direction. Also, it doesn’t look like they have pull starters. As it will be freewheeling, I won’t be able to pedal start. So I’m thinking about a used chainsaw engine. That way I’ll have the shaft on the right, it will turn in the right direction and it will have a rope pull starter. Using the Bicycle Analyzer url from Carl Baron123, it looks like 6000rpm/26in wheel/24:1 will give about 20 mph. I’m guessing it will take a 2-stage reduction to get there. Is it OK to use a bicycle chain for the final drive? Also, what about the possibility of using the derailleur to switch between 2 or 3 gears? (backing off the throttle, of course) Any suggestions, cautions, other ideas? Thanks

Thanks. There's a lot to think about. I'll keep you posted