The Vision is the expected end state, especially as it pertains to the business/user/customer facing end state.
Simple example: Umbrella or similar product
Vision: when walking outside I will be, using a light-weight, easily portable device, protected from sun, rain, wind.
Proposal will describe what product or service the contracting organization will deliver to the customer, especially in terms of measureable characteristics... characteristics defines sufficiently so the customer can view delivery, and the proposal and easily say 'yes' or 'no' to whether the contracted delivery was made.
Simple, relate example:
We propose an device we will call an umbrella. It will be light-weight and will be portable. It will protect the user from rain. In sunny and windy weather it will also protect the user. It will be made of high quality materials that will be water prove and will opaque so as not to allow the hot sun to peak through. The material will be such that it will remain functional in strong winds, protecting the user while not collapsing.
Roadmaps, in my experience have generally been related to products, rather than projects, although in some circles it may be used. My experience of a roadmap would be the plan for product features that would be released to the public at various times.
One simple example Credit Cards and associated systems.
introduction: They first came out and to use them the retailer used the monstrous swipe machine that transferred the image of the credit cards numbers to a carbon multipart form. Your received a copy and the merchant kept copies.
2nd phase or milestone on the roadmap: Magnet strip and magnetic strip readers
3rd phase or milestone on the roadmap: telephone transactions using 3 digit code
4th phase or milestone on the roadmap: online transactions
5th phase or milestone on the roadmap: hologram cards
6th phase : chip cards and chip readers
I am not a credit card systems expert, just a user, but if you have been around credit cards for any length of time, I think you will be able to relate to the concepts in the example relate to roadmaps. The roadmap in the conception stage would show each of the phases or milestones possibly one year apart. If credit cards were know today the roadmap may be as follows:
2016: Plastic cards with account number and expiration date
2017: Phase 2
2018: Phase 3
2019: Phase 4
Finally, I hesitate to perpetuate the term "best practices". Although it is well used, if not overused in industry, there can be no such evidentially sound concept. 'Best' would have to denote something to which the practice can be compared to determine it is indeed the 'Best'. Theoretically, it would have to be placed against every other similar practice and evidentially determined to be 'Best'.