Planeswalker Deck Allocation

Sorry, should have gotten this into the Tuesday post.

When looking at deck builds on TCG, I notice some decks just throw in loads of different planeswalkers/gods (and all the expensive FotM cards) while others just sprinkle in one or two single planeswalker cards, almost for flavor. What's the strategic thought behind both approaches? Obviously money is a big factor for people. But how does one tweak deck viability differently in a 1 planeswalker deck vs a 10 planeswalker deck? I fairly certain that a 4-5 mana planeswalker doesn't work like that odd, expensive endgame spell that you sprinkle in just in case. But how strong can the deck be without a reliable draw on at least your one planeswalker?

I'm just getting back into Magic after a 10 year hiatus, btw, so please forgive me if I'm missing something obvious.

TLDR; PLANESWALKERS, HOW MANY?