You can spend a ton of $ on anything.
I am very lucky to have a Klose smoker with a side fire box. It has a 20" x 20" fire box and the fire box has a removable expanded metal grilling grate on it.
If I want to smoke, I take out the grill grate, so I can add wood, charcoal, etc. and still have the flexibility to smoke.
I would go larger than you might think you need, if you can afford it, the extra room will enable you to add beans, appetizers, side dishes, etc. and still have the room needed to smoke or grill.
You might consider taking a look around locally to see if some one can build you one to your preference.
The reverse flow is a great option, and I wish I had the room to have one.
A lot of people on the forum have more than one cooker, and each one had it's place.
I have 3, the Klose, a stainless MES 40 with front window, and a Weber Propane grill for quick sessions. Each adds to all of our get-togethers.
For some reason, the home boss
doesn't come out in the back yard much anymore. Go figure. Maybe it's because her chair is now much closer to the back fence than it used to be.
Whichever way you go, enjoy, and invite the family and friends, you all deserve it.