I can argue, however, that we should abide by the core book that says "what is not expressively forbidden is legal", and not a restrictive "if it is not explicitly mentioned as legal, it is forbidden", which is what your stance is. RAW, if you will, dictate the first stance, though.
While that is true, it is also interpretation, not RAW. If your interpretation seems unbalanced and a different interpretation of the same rules seems balanced, which is the rational way to go?
Are you fairly entitled to claim a rule overpowered if you choose the interpretation that specifically supports your notion, when a balanced alternative would be available? I don't think so.
Why 9? We need 7, don't we? Although sprites count, and therefore, hjust putting soe into surveillance drones should do the trick.
Max bonus = number of team members - 2
So yes, you need 9.
Diagnosis power, but it seems hard to apply this to tacnets, unless you count it as aiding whoever uses the tacnet. IT'd also add (power*2)/3, not it's power. Page reference would be for the German basic book and as such useless to you, but here you go: pp 236.
That power does not add anything to a device's ratings. It adds bonus dice to a task it assists, nothing more. It will not increase the sensor rating to the nescessary 14.