Ich habe mich erholt.
A verb-second clause (V2 clause). The mich is in mid-field position (where else?).
Hast du dich gut erholt?
A verb-first clause (V1 clause). So we need to arrange the three elements in the mid-field, du, dich, and gut. You have two complements, du and dich. Rule: With pronominal complements, the subject complement comes before any accusative/dative/genitive complement(s), hence du dich, not dich du. (Broader tendency: "active" complements come before "less active" complements.) "Quality supplements" (in the form of adverbs, adjectives, participles, etc) that modify the verbal expression usually come last within the mid-field.
Verabredet sich Klaus mit seinen Freunden?
Another V1 clause. We need to arrange sich, Klaus, and mit seinen Freunden. In arranging sich and Klaus and I'm afraid there are no clear rules as to their position. Generally speaking: (1) Pronouns (including sich, at least for purposes of this analysis) tend to come before nouns. (2) Exceptionally, a nominal subject can take the position of a pronominal subject. If you think about that, it's still not clear whether the sich or the Klaus come first. Both is possible. There is however a tendency to place the sich ahead of the antecedent. It is not so easy to explain that. Some linguists once suggested as part of a broader theory that this has something to do with the "lightweightness" of sich in such cases (it is simply required as part of a reflexive verb and, among other things, usually does not bear the sentence accent), basically suggesting that it does not play in the same "league" as the rest of the mid-field.
Jan hat sich die ganze Zeit mit anderen Kollegin unterhalten. Da hat sich eine Kundin beschwert.
Another V2 clause. (By the way, since you call da a "connector": Da can be a connector (Ich mag Max, da [= because] er nett ist.) However, here it's simply an adverb, which could be translated as "at one point". In this predominantly deictic use, it almost always appears in the pre-field of V2 clauses, as in this case.) In the mid-field, we need to arrange sich and eine Kundin. The analysis is the same as above.