I like to take level 50 as a level to stop training most characters; after all, until very late in the game you can't train past that anyway.

You may have noticed that there are barrels and other events that give a single character a permanent boost to a stat. Late in the game, you start finding things that boost level permanently; these are what I would give to one character.

Remember that, after level 13 or so (don't remember the exact level), XP to level up stops increasing; however the amount of gold required to train continues to increase quadratically. For this reason, it is best to save permanent level boosts until you are done with most of your training.

You might also want to save something like 4 million gold for the southern sphinx.

Note that, if you are still on MM4 and haven't reached MM5 yet, you are way too early in the game to be concerned about this (though saving the permanent level boosts you can get in MM4 might still be a good idea).

Ehh, all guides mention this, but I didn't find not paying to be that bad. Just heal, rest a few times and use teleport as much as you're able, and the traps aren't that bad. Those taxation urns in the dragon caves are far worse – take my character's blood, but leave me my money!