Mac or Ubuntu should be fine, for windows you should use the WSL instructions.
The correct branch for development should be ArduSub-Stable, please rebase your changes over it if they are not rebased.
Since ArduSub uses an old compiler version, the instructions of ardusub official website are not valid anymore, we are working to update it soon, but if you install ARM gcc 4.9.2 it should be fine.
I did a small tutorial in a previous post, probably this can also help you: