My current goal is aiming for just under the 16-bit unsigned integer limit: 65535 ;which affects the client software as a limitation for life and mana bars.
Remembering to leave room for donors, abilities and bonuses; (disregarding the aforementioned) the highest a player can reach before having multiple bars based on Druids/Sorcs at 30 mana per level is experience level 2184.
However, features are extremely important to balance any gameworld. I aim to make the benefit return on botting minimal, and so I combat botters with prerequisite complex quests to acquire level appropriate equipment, the exclusive feature of an extended soul system including weapons and magic that rely on it, monsters that (with special scripting) take a complex strategy, and various other methods.
What about letting the player additionally spend points to customize their character?