I'm going to make some assumptions based on your profile and questions. Are you a seller attempting to do a private contract or rent to own?
If so, you need more help than what anyone here should offer. These are legal questions and laws vary across the country and have recently changed in this area.
Land Contracts are very simple, and very complicated due to the Federal Law. Many of these items may be covered and some may need to be specified in the contract to spell out who is responsible for what. Rather than practice law without a license, I'm going to strongly encourage you to bring what you have to a local real estate attorney to get clarification and protection for all involved.
Sorry I can't do more, best of luck.
2. Seller and buyer should maintain insurance on the home, but an agreement can be made to keep only one policy.
3. This kind of clause is part of the standard REC; review it and supplement it if you find it necessary to do so.
4. I do not think so.