What additional revisions can I make in a journal paper after review, beyond those suggested by reviewers?
Short answer: ask the journal editor.

Longer answer.
I've had two different types of experiences that are contradictory. I've had what I took to be the "standard experience" where one should not make edits to the copy after submission unless specifically advised to do so. In this case, don't make edits other than those that meet the questions of the reviewers. The rationale is that you don't want to introduce new problems during the editing process. 

My sense is that in this sort of case copyediting is usually done by devoted staff at the journal or publisher. Often there are ominous warnings no to go around editing things.

Alternately, I've had a couple of submissions (outside of my field of philosophy) where the editor had both told me the paper was accepted and then made me substantially rewrite the paper, commenting at one point that I should get someone to read the paper and critique it -- which I thought was kind of odd and non-standard since if the paper needs that much revision, you shouldn't say you've accepted it for publication but rather that it needs to be revised and resubmitted...

In this case, copyediting is done by the original author together with the editor in a back and forth manner.

Anyway all of that text to say, these practices are less standardized than you might think and you need to know that journal's practices.