20k? 1400 upkeep, put it as throwing weapon as you said, so you can lower the upkeep by wpf (or put a banner in each weapon category, 1h, 2h, pole).
Make it 3 slot like the pike, the weight and length should fit that.
Boni? Not needed, but without no one would use it on the public servers. Looming it could either lower the upkeep or improve the boni, if there's need of those.
In the screenshot is a quite heavy banner, using a shorter stick for it could make it possible to dual fight with a sword, instead of a shield for example (problem: how to block? In Mount and Gladius they made it possible to block with the banner, thats stupid however).
Its a good idea, just needing a model now.
Flag wouldnt move though unless crpg gets the codes for that.