There is no modification to the cab available to increase visibility.
If the truck is handling bales then visibility is bound to be decreased by the load in front of the truck.
In this case the truck should be operated in reverse.

Don't believe there is an industry standard for truck speed operating inside. This would be the responsibility of the plant operator. Some plants have pedestrian lanes where the truck is not meant to enter. Other areas are no go areas for trucks or pedestrians.
There are quite a few companies that offer speed and zone control. It's an extensive subject today due to the growth of health and safety. However, multi-speed systems are not as easy to have on a forklift or warehouse truck as you might think.