後回し seems to only be used with にする (at least from what I can tell by Google searching), but other such compounds that are formed with the verb stem (Leebo correctly pointed out that these are grammatically nouns) will take simply する to turn them into a verb.
Right, so now I’m back to being doubtful, should I then only use する because they are nouns?Should I only use にする?Is it a noun to noun basis in which case I can’t decide to use one or the other?
I think using する as a rule of thumb is OK. Just remember 後回し as an exception for now. When in doubt, look at the example sentence or Google search for it.