I have mainly Panaques, including a reasonable sized Royal. All my plecos get fed in the late evening just before the lights turn off or just after. They will feed during the day but appear to feed mainly in the evening and at night. Their stable food is algae wafers (3 different brands), veges - mainly courgettes, and of course wood. Occasionally I give them small quantities of high protein foods (blood worms, shrimp, etc.) but only occasionally and in small quantities as their digestive system isn't designed to handle much of it.
Your royal may take a shine to your plants, particularly swords if you have any, and the results wont be pretty. However sometimes they seem to leave them alone. Mine haven't touched Anubias, or Java fern, and I dont think they ate any crypt when I used to have it.
Apparently royals can be fussy feeders (mine isn't) and can go off their food if they are intimidated by another fish.
Give the royal at least one place to hide. Mine has taken up residence under a large piece of wood (the base of a small tree) with a large hollow underneath it.