[oil pan 4]

Hydroboost is from the late 70s at the latest, it is not new.
The steering box by passes up to 15gpm when its in full by pass and develops minimum pressure.
If you try to give the power steering box fluid from an accumulator the fluid will dump through the open passes of the steering box in a few seconds.
When you are not using power assist the steering box goes to full by pass and the pump only develops no more than 200psi.

Do not power the brakes with anything but the master cylinder. I have worked on equipment that uses hydraulic power to actuate the brakes. Just don't do it.
For one the hydraulic brake proportioning valves cost around $800.
Why alter the brake system when you can power the brake booster with a $60 vacuum pump with tank and its a fail safe?
If you lose hydraulic pressure on direct acting hydraulic pressure fed brakes you have no way to stop.
Same thing with the ram steering, if you lose pressure you have no way to change direction.
Brakes that are tied in to the main hydraulic system and ram steering are fine for equipment that moves at very low speed. They are not for a motor vehicle.
This is why all on road vehicles have mechanical linkage to steer the wheels. Its required by law.

How are you going to get a hydraulic motor to move the vehicle?
These are fairly large, very expensive and heavy.
Accumulators are expensive and very big and you have to have some where to put all that fluid when not in the accumulator.

The most efficient brake system is a vacuum boosted master cylinder. You can power them for free with engine vacuum from a gas engine or power it with a vacuum pump.
How can you do better than free?
Then if you EOC you can use a small vacuum pump as a backup.