youre honestly overthinking the fans too much mate,7 is absolute overkill imo.
3 intakes,2 exhausts at an absolute maximum.
personally I hate side fans - the noise etc is not worth the cooling presence - If you use a side fan then make sure its a low rpm model with hydraulic bearing to at least keep the vibration down to a minimum ( & it will vibrate with a side panel with a plexi window)
those silverstone fans are seriously seriously noisy at full tilt (as in unbearable) - I had 3 of those originally in my silverstone case - I pretty much had to replace them asap.