How far can one go in creating new words?

You will find in a dictionary such as the SOED that several hundreds of words created by addition of the prefix "-un" are not listed in the dictionary as regular entries, but instead under the entry for this prefix; only a few are defined but all that are found in that entry are in it because they have appeared in print; a date of earliest recording is included for each. This means that all those instances have been considered acceptable by lexicographers. You do not find "undisturbingly" in this list and that means that possibly it does exist as an already used term and that it has been rejected, although I doubt very much that this should be the case: it's probable that it does not exist as an already used term and therefore it certainly doesn't either as accepted by the lexicographers. Given the plausibility of the concept you are therefore quite justified in coining this term. There are limits in this domain of the productive constructions with "-un", as with other affixes and combining forms. All such constructions do not necessarily result in a word of sufficient plausibility; let's take for instance the concept embodied in the adjective "live" as it pertains to events (live events, ngram). If we do not take into account this criterion of plausibility, which I believe motivates lexicographers in their decision, it seems that we are justified in speaking of "unlive events"; yet the plausibility of referring to representations as events in general does not appear likely and therefore "unlive event" does not appear to be a reality of our world, which precludes the existence of an adjective "unlive"; so, productivity and creation stop here.

Common sense tells us that the only limit not to indulge in, not only in literature but in all domain of verbal expression, is the creation of terms for a concept that has been properly named already, this being done without showing that the new appellation has any advantage over the existing one, except that of providing a synonym (it is sometimes considered that a synonym is useful but the question of synonymy has no clear cut answer).