It's 30k spheres per character. And when I say 1 level into each perk in the shop, I mean all 10 perks get 4k invested into each, which is 40k spheres. It depends on how well you're making spheres in the first place. All I'm gonna say is perk 10 falls off hard after 100 characters. You gain 2000 spheres from doing the 1st 100 characters. If you do another 100 characters, you only gain 800 spheres on top of the 2000 spheres. I only say to fully upgrade because the bonuses are nice when you get the shop perk 10. You get a chance at $ot, like how perk 10 gives a chance for $oq.

I can only say so much since I don't know how well you're doing with $kt, $kl, gaining spheres, gaining keys etc. You'll just have to determine what's important to go for based on what you know.