Scaling back size

Can I follow a model that trades multiple ES contracts, but I only want to trade 1?

Yes ofcourse. Just scale the strategy down , do your own calculations.

you can set max contract to 1(or whatever the number your account size/risk appetite dictates). This is always a good practice and I strongly recommend it, so that your account is not blown up by a trade manager who suddenly leverage excessively ( which you can see quite often here)

Don’t see this option in the Sim environment for a strategy I follow, guess it’s an option when going live?

Dont know abt simu, but for live, definitely that option is available

Yes live is different many options you have .

Sure, but the client can increase max contract to 2, if his/her account grows too. These are often two different things!