‘poka’ v ‘lon poka’. ‘lon poka’ means "by the side of, next to” with ‘poka’ a noun object of ‘lon’ and so needing a pi to attach a two word phrase that means what we would take as the object of “next to” ‘lon poka pi jan pona mi’. ‘poka’ , on the other hand, is a preposition meaning “with, accompanying” and so takes its object directly: ’poka jan pona mi’, which doesn’t require physical proximity as ‘lon poka’ does.
Just where adjectives go in a string is an unsolved (and largely uninvestigated) issue. We tend to follow the habits of our L1 so far as possible. But many choices do make differences it what is said. In ‘jan pona pi kalama musi’, Pije says the person is a good person (‘jan pona’ doesn’t always mean “friend”) who plays music. That does not mean (maybe it implies) that the relevant goodness is in his playing, but that is a bit of a stretch. So that is not very satisfactory. On. the other hand, ‘jan pi kalama musi pona’ is, as a first shot, “a good musician or, at least, a person who plays music well”. If ‘jan pi kalama musi’ is a musician, then we get a good one by adding ‘pona’ to modify the who preceding phrase. On the other hand, playing well is ‘kalama musi pona’, with ‘pona’ an adverb on ‘kalama musi’. The two expressions may amount to the same thing and look just alike, but are different (I tend -- when I notice the problem-- to put a comma before ‘pona’ in the “good musician” case to show that the connection is not with the immediately preceding bit but all that has gone before).
In any case, your version -- whichever it is -- is probably better.