Actually had a mobile setup for a handful of years. Although levers are awesome, it may be too much time/effort for some to use effectively/efficiently. OTOH I'm not a fan of autos either, but most autos don't have to be operated via volumetric controls and can still be controlled manually. I had a 2 group NS Aurelia, which is an awesome/dependable workhorse easily on par with anything on the market. I controlled every extraction manually and steamed every pitcher by hand. I mention that as the Aurelia (model I owned) had two traditional steam wands and a 3rd wand that was automated via a temperature set point. That machine was so well designed I could extract from both groups while steaming wide open (32 oz. of milk) and never lost boiler pressure in the process. It constantly recovered during use and never left me waiting for it to be ready. Granted there are likely other machines equally as impressive, but I personally haven't used one that was. That included 2 La Marzoccos that so many people put on such an almighty pedestal.
For machine selection just get something that will keep up with more than the demand you expect to have at events and has a solid reputation for reliability/user friendliness if you're not that familiar with the equipment/process. Any well designed 2 group HX (heat exchange) should be fine and keep in mind these beasts will need a fair amount of power to be used for hours on end. Generators are of course a great way to power them, but also having an electrical connection if any way possible is much better/cheaper by far.