Have a special challenge for planning ressources in our company:

I have a team of 12 named ressources available.
I'm allowed to use all of them but at least 5 unnamed ressources (out of the 12) must be always free (not allocated) because they must be hold available for unschedules task force issues. And it does not matter who (namely) this is.

So what I want to do the following:

1) Do the planning of the project and check if a dedicated ressources is overallcoated ==> so far so good
2) But now I have to check if the amount of 5 ressources are free over the timespan of my project.

So what I need is the following:

1) a chart where I can see the the free ressources and indicators where the projects allocate more than allowed. Similar to the existing chart "Ressource: Grafik". But focused on the total of the not used ressources.
2) An indicator (like red person symbol in the Info-column) showing the tasks allocating more than the remaining ressouces of

How to do this?
I would be glad to get Hints / Ideas / instructions from you about how I can implement this.

Thanks in advance.
Albert