first off, entrenchment and vanilla are up to v1.16 and v1.02 respectively, so i would start there if you havent already got them.

secondly, just for clarification, at first you said you cant get more than 3 custom maps to show in entrenchment, then you said you cant get any, which is it?

thirdly, i wouldnt bother putting custom maps into vanilla, i have a feeling it has no bearing on entrenchment, so unless you like to play vanilla on those maps, dont worry about it.

next, make sure you have the maps in the right folders. it really doesnt hurt to put them in the map editor folder AND the galaxy forge folder.

if all that does not work. try to download the maps again and save them elsewhere, then, move them into the right folders manually

good luck

edit: you said you put the maps in the galaxy folder right? i think there are subfolders there specifically called galaxyforge, galaxy and mapdesigner, just put the maps in all the folders, i dont think it can hurt.

that way, you have redundancy and can later know which copies of the file to delete and which to keep