I'm sure there are several possible interpretations of your first example. It doesn't strike me as a concatenation of particles leading up to birthday. I'd take "coming on down" as a phrasal verb, as there is a nuance to that particular verb ("to come on down") that is distinct from simply "to come". It's a little more informal, more intimate and also, perhaps in some contexts, a little back-country-jocular. Inflexion is key! And of course, I can't hear you say it, so don't know which box your tone of voice will open.

But as for such concatenations in invented languages, they are a required feature in Queranarran, a language well known for its attention to deictic detail. For example: luluto.saam

from-below-over-top-over-top-down-and-away-ABS-hound-sleepy-MK yester-fox-red-quick-MK EMPH-leap-in.that.moment

The quick brown fox jumped over the lazy dog.

ino-		from below to higher up
soarsoar-	arcking over & above
er-		from above to lower down
arte-		away from