As far as money for potions goes, you can collect all the axes in the catacombs for some pretty decent cash, though finding someone in Aleroth who can afford to buy them is another story. On my latest game, I got my invitation to Stormfist at lvl 7, though I hadn't thought about trying to get there at the lowest level possible. I was almost lvl 5 when I entered the catacombs and even then a few hits from the bigger monsters was pretty deadly. I pumped up my agility quite a bit and still got hit a lot.
I don't know though, it seems like if you skipped the catacombs altogether, got your one free point in restoration, then went straight to do the two army quests, it seems possible (maybe not easy) to get an invitation pretty darn early. Beyond that would get pretty tough. As I recall, Iona's dungeon has a few spots with lots of scorpions, that would pose a major problem to someone who relies on sneak a lot. Though a minor shadow potion would help with that.
Which reminds me, I'll need a few of those at the council hall, since both mummies and ghosts are quite speedy. I can probably round all the main room ones up into one of the other rooms then sneak out of there, then sneak straight for the boss.
Something else I thought of as far as early gold goes, Spoiler?
when George goes to show you his plant, you can loot his stuff, in my game his giant sword was worth over 1,000 gold. That could buy a good ammount of minor potions at the right price.
But yeah, on my way to Ars Magicana I fought the main bully guy you meet on the road just to see if I could, I burned through all like 6 of my minor restorations just to (barely) do it. Then I reloaded deciding it wasn't worth it. So yeah, at low levels, fighting "boss" types that can hit you hard, and that you only rarely hit, that's a major obstacle.
EDIT:
Well I had to give it a try, I made it to Stormfist (with invitation) at lvl 3, but immediately got pushed to lvl 4 when I got the XP for becoming Lord Protector. And by some small miracle (and two minor restoration potions and all five of my minor Shadows) I managed a mad blind dash out of Iona's dungeon lol. Scorpions are a killer. Fire arrows will also take you down pretty quickly. It sucks because you can't use Shadows potions for long due to all the doors and levers. You CAN stand there and regain your stamina though, which is good. I thought I'd have to spend a point on Alchemy to mix up more minor shadows, but it turns out I had just enough (thanks to the magicians overturned cart).
I managed to pick up the "mystery spice" even though I never talked to the cook at Stormfist. Also, if you do Stormfist before curing Mardaneus, apparently George simply disappears without getting murdered.
