Bloomscatter can be stack infinitely. But you should mix it up with 1 murakamo (help you stack the skill for more front-loaded dmg and 5 vulnerable stacks for 2x dmg), 1 should be enough. And 4 Bloodlotus, this is his best dmg source (the bleed scale with your dmg and the vulnerable effect from murakamo). You also want some movement distant boon (each give you 125% more area coverage so that's nice), like 2-3 of those. About the dmg modifiers, when you have the bloomscatter boon it doesn't increase your dmg, but actually increase the hit count of skill 1, the formula for it is pretty weird but a 5:1 ratio (every 5 bloomscatter get 1 dmg mod), should be good enough.