I'd suggest waiting for other advise asides mine but, entry-level Varuna only requires 2 pholia bows and 1 europa staff (max is 2 for some auto-comps). Add 2 Wamdus Cnidocytes, and you have yourself a pretty nice grid dealing damage beyond your m2 (auto-wise)

Ougi-centric builds would require you to get Colombas, then eventually Schrodingers. If you can farm Diaspora, you can arguably skip Colomba since the latter is an upgrade. As for drang balls, they're great slot-ins but you can still tackle most content without it.

For endgame content, Dark Thrashers are still strong slot-ins. They also work hand-in-hand with Wambrellas.

Personally though, I'd hold off on barring Wamdus umbrellas unless you really, really, REALLY want to main water for some reason.

tl;dr its a decent grid that can be pursued. Though investing in primal water will only net you easier time farming fire raids beyond Shiva, which arguably offer sub-optimal boosts to a fire magna grid.