Hi Again El Bisho,
Ok I've given this a bit of thought, If it was me, I personally wouldn't have any BBQ Built in but buy a combo of stand alone BBQs that will give you the versatility in cooking for yourself and your guests.
Build the benchtop possibly with sink and water connected for clean up and prep duties, maybe even a small beer fridge underneath would be good to keep you hydrated and immediate products like butter cool.
I would probably have either a free standing Weber Q3200 or a more traditional 4 burner gas grill for the fast immediate cook-ups...weber Q preferable..but that's just me
so that'll be in the vacinity of around $750
I would keep the kettle for your charcoal duties, maybe buy some accesories for it like the rotiserie and /or the pizza oven set.
(these are usually from 3rd party manufacturers and not from Weber ) except maybe this https://www.weberbbq.com.au/weber-acces ... 00-series/
and thishttps://www.weberbbq.com.au/weber-acces ... otisserie/
Then....to do my overnight low n slow smoking sessions, I would probably go with one of these Traeger Pellet grills. I had one of the earlier made in America models a few years back, exactly the same as Captain Cook has and the same as the larger Texas style model you'll see in the Website. Loved it but a small time of unemployment meant i had to get rid of a cooker.
They may not has some of the bells and whistles of the more expensive models, but they'll do the same job as good if not better.https://www.bbqsandoutdoor.com.au/traeg ... -adelaide/
So even buying the larger 34 model at $1799, with all I've mentioned bar the fridge and weber accesories will set you back between $2500 and $3000, you'll have 3 different types of grills to tackle any type of outdoor cooking.
Just to add, if you want to incorporate any kind of cooking to your bench then buy a proper 3 ring (of holes) Wok Burner. Don't buy anything smaller unless you don't particularly want to muck around with Woks then a small one will suffice but a proper Wok burner will handle anything. Have a seperate cylinder for those.
Now with this set up you will be required to have 3 types of BBQ fuel around....Gas for the Q, Charcoal or Heatbeads for the Kettle and a few bags of different flavour wood pellets for the Traeger. (by the way...Traeger invented the pellet grill originally)
So there you have it....I would arrange them so all the Cookers are side by side 90 degree angle to the benchtop (prep area) and sink. Not knowing how your area will be set up, this is the way I'd have my outdoor area....I don't like BBQs taking up my bench space. But that's just me
Something to ponder I guess!!