Grav + other platform in sub-directory - possible?

So I am setting up a media platform and after initial tests Grav (yay!) will be what I am going to use. I will also have /discuss sub-directory with another PHP platform running (Flarum) similar at here at official getgrav.org/forum.

Now, my questions:
1. How can I make sure Grav won't interfere with my forum sub-directory other than avoid generating any folders/pages with same name?
2. Are there any other precautions I should take for this set-up to work without glitches?

The way a webserver works is that if it finds a physical file at a particular url, eg http://yourserver.com/discuss then it will server that, else it will fall back and use any rewrite rules 'up the chain'.

So, you should have no problem with installing a forum inside Grav. If you are not using apache, and using nginx or something, you will need to manually define the two virtual hosts so that they have the appropriate needed rewrite rules for each.