These four items are the main groups of maintenance I can do for you. Also, they are not all that can be done as maintenance on one website. For a Wordpress website, if you have more plugins, more time is needed for maintenance; and sometimes it has to be updated more often.
How much is this going to cost?
My goal is not to take your money (on a monthly basis), but to teach you how to do it yourself. If you get stuck somewhere, I'll be happy to help you. This only applies to websites made in Wordpress.