Wow dude, one heck of a laundry list there. First of all, if you don't intend to travel around in it then the tow vehicle isn't a factor. You can just have (hire) someone to tow it to your leased lot and set it up. Now if you want he option to travel then a 1500 series isn't going to be your best option. Too little truck for the weight of the units you are considering, especially in the mountains.
Expenses arn't much different than a sticks and bricks home. Mortgage payment, insurance, utilities etc. When people set up a unit for long term living they usually use a larger propane tank than what comes with the unit, 20-30 lb. tanks, and hook up to a 100lb. or so. Yes, go with the all season package if offered.
As far as living space goes, find the floor plan that suits you and works for you. Your needs may be few but once you make the purchase you don't want to discover its not adequate for you and turn out hating it.
Water is the enemy of any structure. A trailer is more susceptable to seams comming loose. With fiberglas sides you can have delamination but you will see it if it does happen. With aluminum sides you may not see the start of any water damage. As to washing the unit, just have a moblie RV wash co. do it 2x a year. Wax it if you want to after having it washed.
Cooking is no different than in a house. The weak link in a trailer is usually the oven. Some say they have uneven heating/incorrect temp. control and things burn. I like cooking on a grill anyway myself.
You are on your own about what insurance carrier to go through. Don't bother joining any clubs like Good Sam. Useless for long term people. Don't bother with the electric stabilizer jacks or tongue jack. You aren't moving around anyway. 6 gal. water heater should be fine for one person.
Don't get a pet if you can't pay much attention to it, even a cat. Dogs AND cats are social animals and need attention even if they can be "self sufficient".
I hope I helped you with your questions.