@JoeMac from the little you have written it is clear this project seems too complex for you to be doing it alone.
Now that being said let me give some tips from some locals I know that have done this EV conversion but they did it for a passenger car not a bus, so keep that in mind.
Ideally for an EV vehicle one tries to put the electric motors either directly into/onto each wheel(directly attached to the wheel like in high end sports cars) or at minimum keep the old axle (if power isn't going to be higher than original engine) and drive the axle (the axle differential reductor) directly , so then the electric motor is located roughly in the back end of what was originally the space for the drive shaft that connected the gearbox with the rear axle.
For an EV you do not need a gearbox nor the old ICE engine so there is free space that one can then use for motor control units and motor power supply/converter/inverter etc unit.
Still it requires quite some rebuilding, you basically have to make a custom frame to attache the motor to the chassis and if you keep the original axle then a custom made motor/axle drive shaft but that at least isn't as complicated as throwing away the whole rear axle and puttin the motor/s in the wheels directly.
If you use a series universal motor (the cheapest and highest power for the money)
then the control electronics are not that complicated, you don't have to do your own boards and IGBT's and all that you can just buy a motor and then buy already made units for the matching motor power rating.
Then the last thing is the batteries, with or without solar panels all EV's need batteries as at least temporal storage units so that as you drive you have reserve power and can speed up if needed. You would need an awful lot of solar panels to drive directly off of them, not realistic. The solar panels can only serve as backup say you go out for a ride in a sunny place like Florida and you drain your batteries, then you can simply let them charge for the day and give you enough "juice" to get to the nearest charging station.
As for the motor power needed to realistically even move that bus, let me give you a rule of thumb.
That motor that you have there with the 48 volt rating, can you lift it up with your own two hands?
If the answer is yes, then that motor is no good for your EV bus project.
You will need a motor that is roughly half the size of a standard boxing bag and it will weigh enough so that you won't be able to lift it from the ground without being a powerlifter/bodybuilder world champion or having a forklift. This should roughly give you an idea of what you will need to look for.
Search for something like a 50kw series motor
A google search of "50kw universal motor EV" already gave some results, some sites even sell ready motors with inverters and wires , a type of "plug n play" kit, that you only need to mechanically install and wire up.
That would be a start, although given that is a bus I would say you will probably need to go bit higher than 50kw.
Around 100 kw is barely adequate power for a normal family sedan, and that is a bus, the weight + rolling resistance is much higher there. I hope you realize the practical implication of this. You will need a heavy mechanical shop with lots of tools to even attach that motor to the bus.
The good thing is that electric motors on average especially universal series motors have a very high starting torque, so even if you install a lower kw rated motor the bus will most likely drive ok at lower speeds. the KW and motor type (pole pair count, geometry, etc) will then determine the maximum speed and efficiency that you will be able to achieve.
