First of all, risks exists in many commercial endeavors.
How does one create a community of users?
A community is created when you promote your cause and when people adopt your programming language. As long as the community, documentation, support and the language itself is to their liking, users will share their thoughts with others and slowly grow into a community. Many things affect this situation and it's hard to pinpoint exactly how to become successful.
To give you an indication; maybe you've heard about Dart, built by Google, I've only heard about it through one of the owners from a start-up. Dart is being promoted intensively and many real life demonstrations and meet ups have already taken place.
What to write the new version in
This is a matter of taste. The team will have to run the necessary comparisons and decide for themselves. Go is rather new, seems to be growing fast as a community; but my knowledge on that matter is rather limited.
Going cross-platform is absolutely is smart consideration. Don't underestimate how big the linux and apple communities are. Even though developing for multiple OS'es is time intensive, ruling out one community might reduce the adoption rate of you programming language.
Forks and licensing
It's fairly easy to create a license for your programming language that allows open-source usage of it, but rules out selling it in the same or a mutated form.
There are plenty of possibilities to earn money. For example to offer premium services, a cloud hosting platform, becoming a premium developer, online courses, commercial licenses, on-site courses, etc.
Open source sounds attractive. However building a community might take a very long time. In order to arrange for fast growth you'll have to convince people to adopt your programming language, provide massive amounts of documentation and help them make the move from whatever language they come from.
Building a programming language with the goal of monetization actually makes the programming language a product. Therefor you would need to create a business model and set up the necessary growth path.