Can you max out your level in World of Xeen without cheating?
It's actually very easy to have more than enough money to get your characters to 200 via the "Inheritance" trick. I did this on Cloud-side. It's a bit complicated, but very possible. First, with the default party (DO NOT yet make your actual party) go to the magic mirror and go to Rivercity. Save, fight, and load if you ever get overwhelmed or killed.
You start near the bank, which will turn out to be convenient, for right now deposit all your gems. Take the back road south of the bank to the River City labor board, where you should work for the money to buy Lloyd's Beacon. Go to the portal and go to Shangri-la. Get the free guild membership, and then at the magic guild buy Lloyd's beacon. Use Mr. Wizard to get back to Vertigo.
In Vertigo, go to the bank and withdraw enough gems to cast Lloyd's beacon at least twice, go to the portal, set your Lloyd's beacon there and go to Count du Money. There you will see a pedestal and 2 piles of money, what hasn't already been robbed from the back door to the dragons lair. Take them and cast Lloyd's Beacon, returning to Vertigo's portal.
Almost done, go to Rivercity via the portal, deposit the 1,000 gems and 50,000 gold. Then go to the labor board, and work until you're 100 years old, it won't take long. Check your bank, you should have around 160 million and 2 million gems. More than enough. Now, go to the inn, make your real party, and you are funded.
I really don't think so, at a certain point the gold exponent simply becomes too high. I can't recall however if enemies respawn in WoX (as they did in For Blood and Honor) if they did then the answer shifts to 'technically' yes. But I'd hardly consider it reasonable.
Most monsters in WoX do not respawn. However, there are certain locations where monsters can, for farming purposes. 1. Nightshadow. Enter the town at night, and the female vampires respawn (low XP per kill though) 2. Castle Xeen. Do not destroy the guard making machine and the Xeen guards will keep appearing every time you ascend or descend the stairs. Use the side towers to farm xp. 3. Sky Bandits (3x cloud dragons). Though the positions where they appear are fixed, the probability of them appearing is random. 4. Sandro if you do not get his heart from the sewers. +100 gems too.
I'm not sure if the monsters in Asp regenerates if you do not destroy the machine, the same for Lord Xeens in Dungeon of Death. I'm also not sure if you can keep ringing the gong in Darkstone Tower to generate Onyx Golems. Those are tough though.
Instead of using the bank/inheritance technique, I am grinding out gold in another fashion, which takes less game time, but a lot more of player's time. I use Sandro to make gems (by this time, I can easily kill him before he attacks me), and then mine out the Gemstone Mines (rolling only for gemstones, reload if gems are obtaineed). I roll for Plate Armour/Mail (for higher profits) at the smiths and then sell. Rinse and repeat. This way, in less than 2 game years, I can get enough gold to train to 200. The XP from killing Sandro is also useful in having the required XP for training. Use the remaining level raising items/awards (Clouds + Darkside, all untouched to date) to reach 255.
It's boring, but you can simply use your current characters for it. I inter-spaced these gold grinding operations b/w stages of Darkside, once I have the ability to safely grind gems from Sandro. This helps preventing it from becoming too boring.
All you need is to have 250k gold for the initial Gemstone Mine replenishment, Sandro's quest uncompleted (and not having his heart in your quest inventory!), sufficient stats to kill him before he attacks (you can use the Day of XXX spells at 5AM to maximize efficiency. You can even cheese it with the Xeen Slayer Sword, which bypass all physical attack resistance). Needless to say, you will have the Merchant's skill a long time ago for everyone in the party.