The main issue you will have is that if the back pressure in the hoist circuit is too high the forks won't lower. And with no load on the forks it doesn't take a lot of backpressure to significantly hurt your lowering time, which lowers productivity. Somehow you need to measure lowering speed and control the load (energy recovery system) to maintain the allowed max lowering speed. And remember that cold temperatures will also negatively impact lowering speed.

This isn't too hard with a pump/motor set because if you know motor speed you know the pump speed, and you can estimate the mast speed. As far as an accumulator goes, I don't think you want to do that. The pressure in the accumulator will rise exponentially. You will need a fairly fast computer to keep the system working smoothly.

ISZ