Vodyani Meta

Well forget the food production techs in science tree. Try to colonize hot planets raise military asap and start oppressing nearest faction. Make a fleet to acompany leechers and exapand as much as possible by using law that enforces 50 approval. Having so many arks will be hard to control so have some fleets on a borders with enemies. The thing is that consuming someone can not be peacful, so Vodyani are military by nature.
Also can give constructive help on luxuries. Sometime i make a mistake and search for the best one which delays my powerspike by additional population+fidsi on arks. Don't be me if you think that luxury is decent  (or even bad sometimes) and there is no way you can get better upgrade it asap. Once enough ark just spam different type of ships you like 1cp/3cp/6p-carrier and start killing and consuming everything that has life in it. Move arks close to enemy so you can easily max out pops with essence and build all industry building, this way you will have a replenishing power right near the enemy. Also you can spam combat arks once you get tons of essence per turn and don't be afraid to lose them if you know that will give you upper hand.

I've only played them once but I definitely can sympathize with feeling behind. I was able to make it up later on though. The early game for me was mostly feeding off minor factions, I fed off the Sophons next to me intermittently, which they didn't appreciate but by the time they decided to step up to an all out conflict I'd had a pretty good military presence going. Other than that I focused my research HARD on colonizing all of the available planets in my systems. Since I didn't know how they worked and that modernization increased the pop cap on planets I was extremely focused on maximizing the space I did have. I dunno if any of that helps, but that's my experience with them so far. My general impresssion of them is that they are slow out the gate but once they get momentum they are a force to be reckoned with.

From my pov the are two ways of playing with the vodyanis, one is the military aproach that was mentioned before. And the other is grow expansion aproach. In wich you focus on getting your lvl4 planetary upgrade as fast as posible (forgot the actual tech name) so you can avhive max pop on planets focusing algo in food prod so you dont have to spend essence to increase pop and trying as hard as you can to mainting the religious party in power so you can leech from enemy planets being in cold war.

The basics are while you are focusing researching the planet upgrade, try to find the nearest enemy and send leechers to prevent them from growing while it boots your growing. Always try to colonice systems with a min of 4 planets. Its also very usefull if you happen to have a few minors factions nearby, free essence and if you can brainwash them a free faction trait.

Once you've got to the late game, even more now with the behemoths, vodyani excels in producing warships at a fast rate thanks to the ark+behemoths fids upgrades, and if you happen to have a 5 lava system fully lvled you can create full armies in matter of two to three turns. From there you can basicaly have every type of victory.

As a side note, this strategy is a bit risky bc some factions who can heavely rush can ruin everything. But if you can pull it of its very satisfactory!

Hope it helps and sorry if i missspeled something. Im a bit rusty writing in english.