Also, can a patent holder decide to not let someone use their patented technology altogether?
Once you own a patent, you own the right to stop whomever you'd like from practicing what it describes. It's yours as much as your car or computer is, for its term.
As such, no, there's no real maximum that someone could charge. Of course, as is the case with capitalism, there may be limits on what people will pay, but that's the biggest consideration.
As for stopping others altogether, that's many patent holders' goals, and it's definitely allowed as well. Of course, you can only stop others from practicing what you claim in the patent, and only once it's actually granted (as compared to being in the application phase), and depending on how broad your patent is, it may be feasible for others to get around what you claim. But barring all that, you do have the right to stop others from practicing it.
You haven't explicitly asked this, but I think it's a reasonable extension: a lot of people who are new to patents get a little confused about what right it exactly gives you. It's very important to remember that a patent does not necessarily grant you the right to perform your invention, but rather, it grants you the right to stop others from doing it. This is relevant in a few situations, but primarily when performing your invention may violate laws, or more subtly, when someone else holds a patent on a necessary step to performing your invention. In those cases, cross-licensing deals can be useful in lieu of (or in addition to) money.