Here are the answers of your questions:
What is the maintenance and support length of time once the license is purchased?
>Basically, we'll supply one year free support, include bug fixes.
Are there renewal costs after the initial purchase?
Future update costs for a new version?
>If you purchase a license of BestSync 2016, the license will work on BestSync 2016 and BestSync 2017.
When Bestsync 2018 is available, your license will be downgraded one-rank on BestSync 2018, and you can pay the price difference for upgrading to your original license rank.