It is not less expensive to travel with a class A than using hotels. I have done the math and only with a truck and trailer could I break even on the trip costs. I do not own an RV because it saves me money. I own an RV because I just love traveling in an RV and for me, it is worth the cost and the maintenance. I can stay in places that do not have a hotel. I have my own bed and a kitchen where I can prepare my meals. I can bring my dog without any worries. It is a lifestyle you either love or not - it is an individual choice.
It is rare that I have any issues finding a campground with open sites. You can call ahead of you are concerned.
There is not much extra work in towing a car behind you with 4 wheels down. We like to spend some time exploring different areas so the toad is a must for us.
There are many good threads in this forum on the tradeoffs between gas and diesel. Search the forums and you will get a lot of good information. There are many factors that go into which engine and what size to purchase.
Yes, it is legal to just purchase one and drive it. I would recommend going to a class or going to the Lazy Daze site to get information. You can practice with cones in a big parking lot.
Maintenance can be an issue. I budget $2200 per year for maintenance which includes changing the tires every 7 years. I do what I can myself and I try and be an educated consumer. I have attended Camp Freightliner and learned a lot of great information about my coach. Yes, there are a lot of systems and there seems to be always something that needs to be done. If that bothers you, RVing may not be for you. For me, I do not know of a better way to travel and see things, and I love doing both.