I understand that your plans are to spend 1-2 years traveling while raising support for your ministry which you are planning to begin in 2-3 years. Your commitment to the Christian ministry, if it is equally shared by your family, will mitigate for any inconveniences that you may experience. Lots of us have proceeded you in the work and many will follow.
A good RV chassis, tires, generator, battery bank, furnace, A/C, refrigerator, exhaust system, etc. would be needed in any unit you choose. You would want to make sure that they are ok.
Most RV are quiet enough, when traveling, to have a conversation needed for school instructions. I have never been in one that wasn't; Class C or Class A.
A Class A will allow the driver's cockpit to be more user friendly for living space. A 29-30' with 1-2 slides will give about 300 sq. feet of floor space and will be small enough to use for shopping etc.. The couch or dinette will provide extra beds. They will likely have larger tanks for fresh water and septic storage. This will be one of you most difficult problems. Most have more basement storage that Class C. They are capable of towing another vehicle or cargo trailer. Bikes would be handy for alternative local travel.
There are many Class A and Class C RV for sale within your budget. Click on RV SALES at the top of this page, also check PPL.com, or Google for 30' RVs.
It would be recommended to plan your travel to minimize stays in cold climates.