I would like to share my elevator design in A18, no mods + floor selector
Basically it is still the good old hatch elevator, but I made some changes so it could work in A18 - elevator system still working as it used to, but the initial push with bottom hatch doesn't. So instead I used powered garage doors 5x3, they basically push you inside shaft. After some tweaks (see prefab/video) it works perfect.
As for floors selection, each floor has powered hatch and corresponding trigger plate on the first floor - when it is triggered, hatch opens (e.g. for 15 sec), so when you use elevator, you stop at that particular floor. You can also use multiple sensors instead of plates in some cases.
I attached elevator shaft as a prefab, here...