L.H.
With all 3 of my kids, I went straight from a crib to a twin bed...never saw the need for a toddler bed, since a twin can be used for much longer. I did see something neat at Ikea: a toddler bed that converts to a twin.
If wandering is a concern, can you put a safety gate up in the hallway to limit his access? Most kids are not going to go far in the dark.
I switched them when the started showing interest in climbing into or out of the crib. I began by putting the boxspring and mattress right on the floor and up against a wall. Then we moved to the bedframe and used a safety rail on the exposed side, but I didn't need the rail for long.
Best wishes!