Is there a limit to how many additional duties a soldier can have, or any other regulations regarding that?

There are regulations that say that additional duties MUST be assigned and who they can be assigned to. There's no limit on duties, that's for the Commanders discretion. In a small unit, or one without a lot of NCOs, it's not uncommon to see an NCO with five or six additional duties. Most of these duties are either inspected during an IG inspection, or critical in that they are required by law.

I do not believe there is a specific regulation that encompasses on how many a person can. That being said, if you have additional duties that are conflicting with each other AND your ability to run your Team/Squad, then I recommend you have a sit down with your Commander and 1SG to discuss these issues and how to resolve them.

When I arrived at Maintenance Troop, RSS, 11th ACR as a Second Lieutenant, my Troop Commander assigned me as every additional duty officer, including Troop Motor Officer.