"I'm setting up my first storm control because I suspect a broadcast issue on a specific interface :"
Well, if indeed 90% of your packets are broadcast, I can see why you believe you might think you have a broadcast issue, but those same stats show a zero ingress rate.
What you also want to know, is what's the percentage of bandwidth being used by these broadcasts.
What you're trying to ascertain, is your broadcast rate abnormally high? Is it beyond what one would expect for the number of hosts and the network applications using it.
The major problem with "storm controls", it's like being in a sinking lifeboat because it has too many passengers. So, to keep the lifeboat from sinking, you start to randomly throw some passengers out of the boat. I.e. your choice is everyone drowns or some drown! (Some choice - not too bad, if you're not heaved out of the lifeboat, though.)
If you have too many broadcasts, first you need to determine if they are valid. If not, find the cause of the invalid broadcasts, and fix that. If valid, mitigate, which might include configuration changes on hosts and/or further segmentation of your network (broadcasts are why we don't all run our LAN network as one big /16).
"I tried to look for the best practise"
Best practice:
Set values well above whatever you believe is the expected normal level of broadcasts, but ideally low enough, your network doesn't sink.
Monitor storm-control getting triggered.
If triggered, resolve cause and/or mitigate to acceptable levels.
