I use banners in both 3 and 4 faction decks. Currently I’ve got a decent working 4-faction Revenge Crown that does pretty well in casual, and has seen some successful ranked use as well, though it’ll never take me to diamond or master I’m sure. Regardless, it actually only has 7 non-banner sigils - 2 for three colors and one for the last.

It depends a lot on what you’re doing with the deck. If you’re running time, definitely go banner heavy, and just throw in 4-8 of some kind of influence fixing, be it acolytes, seek power, that new stranger, or the echo spell.

However, be careful that you don’t weaken yourself too much against fast decks when going heavy on banners - while you get influence far more consistently (especially necessary if you have cards that cost 2 influence of a single type), you tend to slow your opening game down.

That’s not necessarily bad - my Revenge Crown runs both Celestial Omens and Harsh Rule, as well as plenty of 1-2 cost Revenge chumps. I rarely have an issue surviving to turn 5 to drop that harsh rule - and I’ve got enough draw and mana fix to get there if it’s in my opening hand.

More competitive decks use this same method, too. TJP control and big combrei back before they became less common liked to use a combination of ramp, Sigil digging, and lesser empower creatures to draw fire until they could power a harsh rule or Marshall ironthorn.

So that’s kind of the key to massive banner use: Make sure you have an answer to a slower start. Assume your opponent will very likely have stuff on the board before you, and up your level of removal in your deck - fast spells if you can, and the cheaper the better.