[Firestormalpha]

From what I've read, the maximum level in Diablo 2 with the expansion is 99.

Because of the way the maps are supposed to be randomized your caves to the North could be East in my play through.

The problem with taking your hireling into a higher level area is the risk that the monsters will swarm and obliterate them before they can gain any experience. Though unless you plan on just blitzing through the whole game, it's very unlikely that you'll run into such a situation.

Not sure if there's really a "strategy" to level up your hireling. I've found that as long as I keep their gear updated and revive them as soon as they die (return to nearest town pay the mercenary contact money) they keep level with my character pretty consistently.