Hello. Let me answer your questions:
1) As a solo user, you can apply to the Personal Edition at https://www.plasticscm.com/download/request/requestpersonal. It has some limitations compared with the commercial editions, but it you don't need those features, you can use to develop and sell your game. On the other side, Community Edition is only available for OSS projects and Non-profit Organizations (NPOs).
2) If you collaborate with users that only do updates/reads, and not check-in's/writes, that users doesn't count as active users, and are free. Otherwise you will need to move to a commercial edition (Team or Cloud).
3) For a solo user, Cloud Edition gives you the advantage of the cloud storage, that depending on the size of your repos can be something to consider or not.
4) The Personal Edition is an on-premise edition. Therefore your repos are local. You can combine with Cloud Extension, to move or replicate them to the cloud. That extension is not free.
5) Gluon GUI is designed for artists and not professional developers. It is only available in commercial editions (Team or Cloud).
You can test a free-trial for 30 days (Team, Cloud or both) at https://www.plasticscm.com/download and determine if the Personal Edition is enough or you need to move to a commercial edition,
Plastic SCM Team