Lvl idk it depends on build, 24 level is no prob in few hours max.
Gear..
-for vs encounters (when they focus other monsters, not you) i think lvl 1 is engouh, you dont need even armor and some basic weapon (i was doing them fine with flamer and without armor)
-for ghoul only encouter .. i believe you need 20+ lvl, metal/combat armor and some effective weapon (grease gun is fine, easy to craft both weapon and ammo, hex them one by one), if they are scavengers then focus one with molotov cocktail
it all also depends on your build.. they are doing alot aimed attacks so high EN is recommended to be not knocked down so often, i died there alot times even with CA because i got just 6 EN and was perma knocked
also if you want to push your xp hard then craft tons of 5mm ammo and rush them with avenger