You have to forefit some of five tags, because even if you insert them in the body of a message it counts against those five tags. How #payitforward works is described here, how #minnowsunite works is desribed here & here, I also think that someone has some bots that visit minnowsunite tag, but I can't seem to find the post about it. With this whole thing about someone using bots to sell upvotes it could be no longer a thing or relevant.
#spreadthepower is tag for contest creators as well as others who offer any services and shows that they give/accept payment as SP, partially or in full. It is fully explained here.