After completing 1 order you have to cancel the job and then take a new order.
If you try taking a new order after completing the first one it shows an error "someone is already doing this order".
You have to click cancel order and then start again to do another job, rather than just being able to choose take order again.
Also if you try taking another order while sitting in your forklift you will fall through the floor and become invisible until you get out of the forklift.
Tried this out since you added the changes, one thing I can suggest is:
Add peds to use qb-target so it has more RP to it, otherwise you're looking for an invisible spot (this is more for use on maps that isn't that expensive paid one.
Add ped for garage, but make it so when you choose "Get forklift" or something, that the spawn for the vehicle is obviously not on that ped, so you spawn into the vehicle away from it.
Change the truck so it takes math.random ammounts, at the moment it seems to take one only, but would be cool to math.random it.
What happens at the end of delivering a pallet and the truck goes? I drove forklift back to the sport to put it away but it doesn't allow it (I assume due to the qb-target stuff)