I remember a BBS door game, back in...well, back when we had BBSes and they had door games. I don't remember what it was called, either, but I do remember that you could carry up to 999 healing potions, and drink as many as needed as a free action between turns. Combat went 'hit enemy for 284 damage, get hit for 305, drink 7 potions, repeat'. It wasn't battle. It was inventory management. If it couldn't take you out in one hit, the only relevant question was whether you'd drop it before you ran out of potions or not. PvP fights were about the same - you and your 999 potions vs. him and his 999 potions. Even if you had a clear advantage, it was a long, boring grind. If it wasn't, it was a battle that was won not by swords and magic, but by whether you used a 50hp healing potion when you had 49 points of damage, or just waited.
Maple Story is similar. You can carry thousands of healing items. If a monster can't one-hit you, the only relevant question is whether you can take out enough of them for it to be worthwhile (and it's usually a matter of whether you get 6% or 9% of a level per hour, which is another rant...), and whether you're making enough money to pay for supplies.
Final Battle Adventure Online is not an inventory management game nor is it an economics game. I don't like inventory management games - I remember playing through Baldur's Gate II and it regularly taking upwards of half an hour to move items around. My wife asked me why I bothered playing it, and I couldn't come up with a good answer.
Anyhow, the main limiting factor shouldn't be inventory space or money. I think the main factor should be HP. Money will always be a factor - you can get better stuff and take less damage per enemy, but it won't be a matter of purchasing huge amounts of healing. If have to decide whether you can afford the 400 turkey dinners every hour that you need to eat to stay alive, then the game is doing something wrong. If you can eat four hundred turkey dinners in an hour, the game is doing something wrong. Yes, it's a game. You're fighting giant slime bunnies. But if the main bottleneck is how fast you can eat, and you can eat and fight at the same time with no penalty, then there's something wrong. That's why I want healing potions to be rare, difficult to get, and have a cooldown period. They wouldn't be available in shops, but may be (repeatable?) quest rewards or such.
I also don't like games where you have to sit around and wait for a long time to heal - sitting around for a long time isn't fun. So, how do you heal and when?
Firstly, being in town fully heals you. Secondly, some dungeons will have healing spots. These healing spots will require jumping, climbing, intelligence, listening, or whatever other stat/skill we think should do more, so that way you don't need to go all the way back to town to heal. Thirdly, there are clerics and other folks with a limited number of healing spells. Fourthly, if you wait, you're healed.
Automatic healing happens when you're not in combat. Every 15 seconds, you heal. First 5%, then 10%, 15%, and so on. So after one minute, you've healed half your HP. If you can find a place to rest for a full minute or two, you're healed. Let's say healing happens a bit faster in 'safer' areas and a bit slower in less safe areas. So, outskirts of town, you heal every 5-10 seconds. If you're trying to rest up in the middle of, say, the Glacier Dungeon (or Lava Dungeon, or the Zombie Slime King's throne room), it may take a while. So you can either try to find a place to heal faster or wait it out and hope that there aren't any wandering enemies.
So it's a matter of how far you can push yourself and still be healthy enough to either win or retreat. There will be some dungeons where it's a lot easier to get in and grab the treasure than it is to escape with it. It'll be fast-paced and dangerous, because it's more awesome that way.