Starting from the second floor, there’s multiple elevators so I numbered them. Each elevator corresponds to a starting point, so riding E2 will bring you to S2. The shape and scale of certain hallways are off due to lack of space/sense of distance. After the boss fight on F3, that area becomes your new “home base” where you can switch party members/rest. Right before the final boss, there’s a rest point but not the other services available at home base.
There’s 3 consecutive fights (4, if you count the last one where you cannot lose). You get full healing between the 1st and 2nd fight, but that’s it. If you’re sufficiently leveled (I was around level 38), have Earth Wall (makes 3rd fight MUCH less painful) and found all final equipment in the dungeon, you should do fine. To be extra safe, I had Kloe to heal and Olivier for backup healing, spamming Earth Wall, and dealing damage during safe turns. Joshua should use Clock Up EX on everyone, and Estelle should use Morale to boost strength. Then spam all your powerful Arts (because like most final bosses, it takes more damage from magic than physical attacks barring S-Breaks).