Go for a QS hub motor if you can. They are reliable, cheap and powerful, so it's basically a no brainer here. IMO, hub motors are the way to go, they don't use space, they have plenty of torque and they are quite efficient. Unless you plan to use some kind of gearbox, there is no point using an inboard motor.
For the battery, your plans seems ok. If I were you I would purchase a ready to be used pack or tailor made from a decent expert, since building your own is quite difficult, the time you'll spend on it, plus the probability of screwing up, giving up, doesn't worth to make the effort (in my opinion). Especially if this is the first time you're building a lithium pack, you probably shouldn't directly tackle high power applications, any screw up can potentially be dangerous and costly.
About the controller, it will mainly depend on what you plan to use as final battery capacity, voltage and C rating, plus the weight of your machine, your own weight, wheel size and motor characteristic. In my opinion, decide first of what battery you'll use/you can afford, and then it will make the other choices more obvious.
The positive point is that this chassis seems to be lightweight, with potentially enough space to put a good battery. You can expect great performances with this, 70 mph shouldn't be an issue at all, with very good accelerations.
You can have a parallelogram shaped battery up front and put the controller in the triangular shaped space in the middle. Could look good if you do the job properly.
Again, start by defining your battery: contact suppliers and define your maximum cost for this element, then see what is available. If you have doubts about different batteries offers from different suppliers, we can help you decide
In my opinion, you should go for at least 72V, ideally 100 or more, with a minimum capacity of 50Ah, the more the merrier. I have no idea how much this could cost in the USA, here in China I guess it would be around 8000 - 10 000 yuan or so for a 100V 50Ah LiFe.
Good luck in your project, the most difficult part is to actually make the first step and start it!