Preferable the the one with the highest rank.
In many monasteries in the ancient times, they had no resident priest, so one without order presided. So did the hermits.
I do not know about the incense. Incense should be blessed, I do not believe that anyone but priest or bishop has right for this blessing. I ma ye wrong, but according to the canon law the permission had to be explicit;
Can. 1169 §1. Those marked with the episcopal character and presbyters permitted by law or legitimate grant can perform consecrations and dedications validly.
§2. Any presbyter can impart blessings except those reserved to the Roman Pontiff or bishops.
§3. A deacon can impart only those blessings expressly permitted by law.