Hi, fab idea - you’re right to start planning early! We have done 4 European road trips like this (one was Germany, Switzerland Italy!) and several ski trips over last decade. We have always driven our car - we only have a medium sized boot so I make sure we stay somewhere so we can run laundry twice during the trip, and we therefore just pack the bare minimum.
I use various sites like booking.com to find hidden gems - we’ve stayed in some gorgeous places that are a little outside the main tourist zones for <eur120 per night for all four of us - sometimes we manage two bedrooms and sometimes we are sharing one large room. Hostels would definitely open up possibilities if you are prepared to use them!
I absolutely love planning trips and researching interesting places to visit though, so I’m happy to invest a hundred hours+ setting up a holiday itinerary. I would recommend picking a few key places where you really want to stop, eg Phantasialand or GardaLand, and then think about logically where your nights will fall - do you want a few long stops, or happy to move about a bit more? In a two week trip I find 5 different places is about the max I can handle - so I would usually make one long stop say 5 nights so you can relax and enjoy activities, explore more fully one area and I usually find a long stop handy for doing laundry and keeping self catering costs down (if you can plan 5 days of food, it’s more efficient than shopping day by day).
The thing about a motor home is if you want to take a day trip or pop to the supermarket or to a restaurant then you’re limited to small trips by public transport/on foot or going in your motor home, aren’t you?
Camping is do-able …are you experienced campers with all the kit, and do you have a suitable vehicle?