Although as I got further along, I did my best to just use something existing from the MM, and re-skinning that, maybe with a minor tweak (e.g. That was a fair bit of work, especially at first, because I found myself statting up a few of new monsters. Personally I've run a whole Adventure Path, level 1-20, Age of Worms, which I personally converted from 3.5 to 5e. I'd advise doing enough for 1-2 sessions, and doing as little change as possible that might take a couple of hours, assuming you know the 5e rules and have the monster manual(s) to flick through and find roughly equivalent monsters.
