Some units built before Thor bought them all up were built better than today's new units are. Maybe look for a well taken care of 6-10 year old unit. Like @dryfly said, unless the owner fixes most things himself it will spend a lot of time at the dealer and then most repairs aren't done like you or I would like.
Ours was built by Keystone before they were purchased by Thor.
I was pretty handy and could fix a slide gear, added LED lights just about everywhere, built a tray to hold our generators and many, many, other repairs. Remember, when going down the road the 5er is experiencing an earthquake.
We have a Ram 2500 Cummins with a 33.5 foot fifth wheel Sandpiper by Forest River. It is more like 36 foot long so don't be fooled by the model length. New Rams have an excellent built-in fifth wheel and goose neck setup. There are several aftermarket and OEM hitches available for the truck. I have a mega cab which only comes with a short bed. The trailer hitch weight needs to be over the axle. But when you are maneuvering the trailer could hit the cab so a slide hitch would be needed to slide the trailer aft for maneuvering. This is not a problem with a long wheel base.
I think 35 to 40 ft. Rigs are ideal. My wife and two large dogs are comfortable in ours. The Sandpiper is an entry level rig. It has high quality equipment assembled by rookies. There are only a few companies that build reefers, air conditioners etc. so the equipment is similar regardless of trim or price range. I like the idea of getting one with king bed standard but getting the queen instead. If I were to go full time, I would look for the largest reefer, 50 amp service, dual air conditioners, independent slide controls, large basement storage, and large tanks.
I think your camera sizes will have to go down, but wiring beneath the rig will be easy. Maybe invest in a mechanic's creeper. Also, keep in mind that they will complicate things when traveling.
these quick "5th trailer" review pages suggest 36' is optimum size due to weight, easier to tow, etc. Anything larger starts to get into more luxurious models. Maybe it will all boil down to how much I have in my bank acct. Some of these campers, even in the 38' range, are $100k. Didn't expect that.
There is no "optimum size" or "one size fits all" trailer. Everyone has their own likes and dislikes. Why not just go look at different sizes and decide for yourself what you like? One person may say 30' is great, and the next will say 40' is great. You will best be served by the size that meets your requirements.
If you are not going to travel around then you can probably get most 36' 5th wheel trailers to your friends property with a 3/4 ton diesel truck.