I think you're a little confused on the purpose of a machine polisher, a machine polisher is mostly used with abrasives to remove larger defects like swirls and deep scratches from the paint, along with it can be used to apply sealants but doesn't really benefit this.
A new car can require polishing immediately, there's many reasons why including scratches, sanding marks from factory etc.
You specified sing bilt hamber cleanser polish, this is a polish meant to be applied by hand there are different polishes for da machines, BH Cleanser is typically weaker as it's meant for hand use.
But to answer your questions:
~Is it safe to use a DA machine polisher to buff the polish and wax as required, every 6 months?
No, you only want to polish a car when it's required as you're removing clear coat every time. Wax should generally be applied every 3 months and is best applied by hand.
~Would using this often wear the top coat?
As above yes, if you want to get technical you can use a paint gauge to see how many microns it removes from the paint.
~Is it even if any real benefit? Time saving? Better/more even coverage?
Massive benefits in looks and time savings to comparable time spent or correction levels, coverage would be the same.
~Any advice or tips on using for this function?
Watch lots of youtube videos on it (Larry at Ammo NYC does great ones) as I think you need more knowledge on the process, before committing to investing money into it as it quickly breaks the £200 mark for the required extras.
~All recommendations are welcome….