So, how many levels does the freaking iron mine have? I've been going in and out of it for over an hour, used up 2 genie boxes already and have made it down to what I think is the 6th level (definitely beyond 4 now), and I have no idea how much deeper/harder it will get =/ Have I already passed the main quest point and the rest is for other side stuff, or do I need yet another trip to town to stock up on more health potions to get down further?

My main goal at the moment is finding that portal back to the surface, to make things easier... But judging by how deep this is already, I have no idea how much further that will be.

I think it's 7 or 8, I'm leaning towards 8. You have to touch it once to activate it on the other side so if you're brave and quick you could run to it (hold your party) and then just return when you've repaired, bought new potions and whatever you need to do in town. As always, especially if you try this, save often and with cumulative saves, not just quick save.

I ran out of health pots maybe twice. It's the deepest dungeon in act 1. Others are usually 1-2 layers deep.

As for the health pot issue they included a "checkpoint" system in the game, namely the magic boxes you get in the lower levels, 1 / layer if I remember correctly. Just destroy these, talk to the spirit and get him to shop with you. Repair your item and buy as many health pots as your inventory can take (not joking, max it out). Just pick up items that are magical and throw the rest. Before long you will start getting rich, I started act 2 with 20k gold and I didn't bother with looting arrows, only throwing items as they sell for much more when enchanted and before long I was pretty rich.

Also some of the final quest turn-ins give you quite a bit of money and good items, make sure you save before handing in quests and if they give you a good item and the stats are bad (i.e. + int if you're a paladin) just reload, rinse and repeat until you get a good item.

A bit more than you asked for but I hope it'll help you with things farther along.