I have/had a 6 inch, 8 inch and a 12 inch dob. The twelve changed from tube to truss as I changed from 40 to 60. The steel tube 12 was not much of a problem for me when I was younger (6'5" and 250 lbs.) even though it was awkward to carry. I had an Orion case that allowed me to drag/slide it through the house easily and a hand truck for delivery to the vehicle and viewing site. Best thing about the case was that it kept dust off of the scope while not in use. I could stand it up vertically and not sorry about crud settling on the mirror. Bugs couldn't get into it either. Most of the time it was hand carry. Back seat of the F150. Base in the truck bed. Worked fine. The base of the Orion 12 was more of a pain.
The difference between the smaller dobs and the 12 is like chicken salad vs. chicken s___. Only super dark skies reveal any real depth in small dobs. I think the 10 inch dob is the best compromise between size and weight for the average sized person, but I don't like compromises! While lusting after a larger dob (16-18 inch truss) I content myself with a 12.5 truss as my retirement scope.
Buy the 12 steel tube and don't look back. When and if it becomes a burden to transport and set up change to a smaller rig but chances are you will move in the other direction to a larger dob first. Only you can know for sure. But I do know that you will have a BLAST with the twelve for a long while.
I second the vote for a Panoptic. Get a decent cross haired cheshire/sight tube and quality laser or autocollimator. Use it every time, it only takes a minute in the field. Get a Telrad too. And the Jumbo Pocket Sky Atlas or SkySafari Plus or both. The chair can be a stool at the start. Harbor Freight boxes for eyepieces and finder/collimators. Dew becomes a problem for the secondary way before the big mirror - small fan will keep it under control or get a dew prevention kit. A few hours will pass before dew sets. Small newts dew up much faster. Get cracking and order today!