How do i increase my banner stats?? Is it by allies or my actual spy stats increasing due to buildings??
Your banners stats are percent based, and use your building stats to increase. More buildings, and better buildings, will increase the stats your banner gives.
Not really, considering that by selling a spy building he'll indeed use less spies per action, he'll also have a lower overall number of spies. So there really wouldn't be any difference.
I would guess even more, using both crux bonuses and a br bonus, I made around 700mil first hit, and I'm not even close to bc. Factoring in 50% ee bonus, 15% br bonus, 300% from both cruxes, then the end of event plunder bonus, bc would probably easily make over 4bil first hit.