Why aren’t there any books in the prison library

At present I would argue that there are no long term benefits to accepting higher risk inmates, although there is a small short-term benefit.

Alpha 30 changed the way you get paid for your prisoners. You now get a fixed $150 per day for each prisoner regardless of their security level. You get a larger one time payment for higher-level prisoners but after that you receive the same $150 you would receive for a minimum security prisoner. Because of this there is not really a risk/reward trade off like there used to be when you got paid more for higher levels of prisoners, just more risk.

I usually start by only accepting minimum security prisoners. Once you have things set up medium security prisoners usually are not too much trouble as long as you keep their needs satisfied and any prisoners with a "Snitch" or "Ex law enforcement" reputation in protective custody away from them in. Maximum security prisoners on the other had can be a big headache. Especially if you get a "Legendary" prisoner in, they will cause problems; you will most likely have deaths, eventually your guards will kill him and/or he will kill some of them.

If you need some quick cash you might want to accept some maximum security prisoners since you get $1000 each for them (as opposed to $300/$500 for minimum/medium) but long-term I would avoid them unless you want to increase the challenge of running your prison.

For a delivery area to be considered valid - and thus a stop for the truck - it has to be connected to the curb of the road. (That is, one square to the left from the actual road.)

Your fenced-off delivery area is in a valid position and therefore the truck stops there to be unloaded. The workers, however, cannot access the truck, as the position next to the truck is blocked by the fence.

If you remove the fence, your truck should be accessible and unloaded appropriately.