The ShiftstonedEternal Power Calculator is a deck-building tool that visualizes your odds of drawing enough Influence and Power based specifically on the cards found in your deck.
I think you really have to play seek power here. Diplomatic seals just won't cut it. Might have to play a couple trilands just to make sure you have enough yellow sources. Could play 10/3 shadow/time, but might be too low. kinda sucks to not have insignias
You're right that diplomatic seal is not a card you want in a deck with tasbu. However, if they cut the dip seals for shadow sigils tasbu should be easily castable on 5. Trail maker helps a lot. 4 Vara's favor is excessive though, they probably want 2-3 favors and 1-2 seeks.