What do you think about putting two Grin All-Axle Hub (one in front wheel and one in rear wheel) in 72v.
Keep in mind unless they've finally finished the new version, the GAA doesn't have a place to put anything for a pedal chain drive, so you won't have any human-power options. You can still make yourself (or have made for you) whatever axle and spacers you need to mount a front GAA on the rear, but it won't be a bicycle that way, it'll be a moped or motorcycle by most local laws, if that makes any difference to your usage.
- Is 2000W 72v the max I can reach by motor ?
No. You can reach as high a voltage as you like as long as you can fit the battery on the bike, and you can afford the controller to run it from.
You can get as high a wattage as you can afford and physically fit on the bike--it's determined first by the load you will put on it (since you'll only draw as much power as your load demands), then by the battery's ability to supply current without sagging much in voltage, and then controller's ability to supply current. THe motor also has to be able to shed the waste heat from the power used, and generate torque with the current provided without saturating (which means effectively the rest of the power used is made into waste heat).
- Do you have an rough idea about the acceleration and max speed for these two 72v motor configuration ?
For this, you can use the ebikes.ca motor simulator, along with the necessary info it will ask for about your riding conditions and bike and total rider+system+bike weight. Instructions on using it are below the chart. Experiment with it until you get a system result that does the job you want according to the chart, then below that it will show you what your battery will have to supply, and how much the motor will take, to do the job. It will also show you the approximate wh/mile you can use to estimate range with any particular battery.
If the battery you have can't supply all the power the simulator shows you need to do the job you're building the bike for, you'll need to buy or build a new battery that can, or else the bike won't do what you want it to because you'll have to either use smaller controllers than you need or limit what bigger ones pull from the battery, so that you don't damage the battery (which could lead to a fire in the worst case; poor system performance and faster battery degradation and aging in the best case, with a range of other problems in between).
- What controller I should use
That depends on a few things.
First, you will need two, one for each motor.
Next, the simulator results showing battery power and current and voltage will tell you the ratings the controller itself must have at minimum. Getting one that is better than that, and limiting it's battery current to what your battery is able to continuously supply will probably give you more long-term reliable controller operation, but at minimum it must be able to do what the simulator shows.
Next, you have to decide what features and functions you require from the controller.
Do you need it to be programmable? If so, what specific things do you need control over? The more programmable it is, the more programming you will have to do to get the system to work properly, the more tuning to get it to do what you want.
Or would you rather it be plug-and-play, with no user-setup required? (you lose the ability to change things without replacing the controller in this case).
Do you care how loud the motors are, or how efficient the system might be, vs the cost of the controller? If you need cheaper controllers you can get common trapezoid (square wave) controllers; they'll be noisier and less efficient to a degree. Slightly more expensive in some cases are basic sinewave controllers, quieter and sometimes more efficient by a tiny amount. More expensive but much more versatile and efficient are the FOC controllers.
What specific features do you want it to have? (look around at as many controllers as you can, and see what they can do, and note down anything you see that you want your bike to be able to do, or that you want to be able to do to / with the controllers).
Do you require a display? What specific features must it have? (displays are generally controller-specific, so to get some display features you may have to give up some controller features since you generally can't mix and match, with a very few exceptions).
You know you want regen, so...there are several ways it can work.
The most common is just on/off at a preset amount of battery current per volt. That means that you are either braking or not braking, and have no control over how much braking force there is, which is not safe in some riding situations (wet roads, mud, etc--anything with loose surfaces) because you can lockup the wheels and lose all control over the bike. Most of these only regen within a certain range of speeds, with no regen at all at slower speeds, and will regen harder at a higher speed because they don't regulate the braking current (except by turning regen off if it exceeds a non-changeable limit) and usually have no user-settings to modify any of this. Usually no regen when the battery is above a certain non-changeable voltage, either.
Next there are some that let you change some of those settings, but are still on/off.
Next there are some with variable (proportional) regen, that don't let you change any settings, but use the throttle to control braking amount. Some of them you have to engage the brake lever first, and some it just brakes if you lower throttle below the amount needed to maintian the speed you are at (unless you just drop the throttle to zero quickly, to coast).
Next there are some like that but that let you change some settings.
Next, there are the FOC controllers that generally give you a fair bit of settings control to customize braking to your needs, and that all have variable regen. Some use the throttle as previously described, and some have a separate variable braking control input you can use another throttle for, or any other variable control. These also usually can brake down to nearly zero and sometimes even to zero, by not just regenerating current from the spinning motor-as-generator like the others do, but by actively reversing current flow to the motor to force it to slow down faster, so they can brake harder than any of the other systems.
There are a very few of the non-FOC controllers that can actively reverse current to the motor, but they aren't monitoring the motor current (no hardware for that) so they can blow themselves up or damage the motor itself or phase wiring by rapid overheating if you do a lot of hard braking frequently or continuously.
There are other considerations for which controller to use...but you have to determine the job requirements first, then decide on your required and desired feature sets, before going further.
It's very likely that you won't be able to get every feature / function you want, so when you make your list, prioritize them by things you have to have, vs things you would like to have.
when quoting (and possibly when reading it?).