Correct, standard subscription is one GUI, one Render Node, so that covers you for opening Max/C4D and using Corona and rendering on any single machine (the one you are working on using the GUI, or another one if you so choose, so long as you don't also render on the one you are working on :) ). The end examples in the blog cover this.
Correct on the 10 artists and 5 computers as a farm (assuming you mean 10 computers used by artists to work on, with 5 other machines off in a corner somewhere only used for rendering). The end examples in the blog cover this.
Correct that if you have an existing subscription, and keep it renewing, you keep the same render nodes (and pricing) that you currently have. There is no mention of whether this is "indefinite" because in 10 years, who knows what the situation may be - the same pricing and nodes while continuing to renew is the plan for now, with no date or plan set or being considered for that to change.