It looks like a decent basis. Could you put some pictures of your actual bike so I can see how hard it would be to fit a hub motor, especialy the swing arm?
Nothing wrong in using hub motor on a motorbike, it has been done a lot of times and it works very well. It can easily outperform the original gas bike, by far. 45mph will be easy to reach, and given this low figure I believe your expectations in terms of power aren't really high... so you'll probably be surprized!
You didn't mention any budget, so I'll propose you a setup that I believe is affordable and provides decent power. Get a QS hub motor, at least a 3000W, preferably 5000W, and if possible with the aluminum rim, not the ones with spokes (they heat more and they are less reliable).
For the controller, you should be happy with anything having more than 150A battery current/350A phase current. That won't be crazy powerful, but probably more than what you think currently. If you want a decent setup and you have a few more bucks to spend, try to go over 200A battery/450A phase.
I can't really recommend any brand since quality is always unconstant. I personnally like the Sabvoton controllers, but recently people say that they are less reliable, so you could also consider other manufacturers like Kelly, Mobipus, Votol, YuyangKing...
You'll also need to make sure your battery will be able to supply that kind of current.
Anyway, please describe better stuff like your budget, and intended performance, it will be easier to help you.