I hadn't realized the nerf was so heavy handed!  So what is a voydani player to do if there are no minor factions nearby on spawn.  That seems more crippling than any start I have had with a craver playthrough.  I have seen a few individuals note that you can use essence modules on your arks but that nets you 40 as far as I can see which seems lackluster and detrimental considering you are giving up production mods.

The essence conversion is worthless. It's never worth it over spending the essence on a new ark.

You have to trade for manpower with other factions and build siege fleets with bombardment modules which has to bomb the planet to 0 defense before you can invade. You also don't really have to invade at all. Parking a leecher fleet above the system is enough to get you most of the benefits.

With the Vodyani you want to avoid contact with other empires till at least turn 100 (depends on map size) 

Since they have arguably the weakest start out of any faction in the game, maximize industry and dust production so that you can pump out ships and upgrade your 1-3 early game Arks. I've played 4 games as the Vodyani on Endless difficulty and I always build essence and science modules on my Arks first. (the essence modules can come in handy when there's a lack of minor factions around and also provide bonus essence even when there is). 

When dealing with minor factions, you have two options, you can either start immediately leeching essence from them, or you can build your "relationship" with them to the max, brainwash and then they'll provide essence without the need of a leecher ship. (I tend to go for the latter, even if it sabotages my early game). 

Also, the Vodyani have a really powerful star system defense in their arks, so you want to upgrade them to the latest military modules (beams work best in my opinion) constantly so that they stay ahead of pirate and major faction fleets. 

You want to destroy pirate lairs as quickly as possible b/c once they reach level 4/5 they'll start spawning fleets that can become a nuisance to your systems and hinder your fragile economy 

Overall, try to avoid having contact with other major factions until you have a large fleet, and try not to rely on minor factions since they provide a good source of dust/manpower/essence in mid->early late game 

Be careful about building the patriot pills plants and the food rations system improvements since the Vodyani struggle in food production with the -50% trait and it could lead to losing instead of gaining pop. 

Lastly, take advantage of the fact that Arks can change systems, it's often good to "turtle" in a way, by going to a part of your constellation that only has one or two-star lanes leading to it and then blocking those lanes with fleets and offensive Arks (hard to keep track of but it takes a lot of juggling the modules on your Arks and they can turn into powerful early-mid game ships before you get access to carriers) 

Just in case you find this strategy slow going, the alternative is to stack all must serve on your arks, research the upgrades to the arks asap, and relocate yourself near another civ or minor with multiplanet systems. Youll find any science is compensated by your ability to speed through buildings and upgrades. Be mobile, dont be affriad to move. Build ships and protrct your leechers early. Shipbound has a very important meaning here. No other factions performance is directly tied to ships as much as the vodyani. 

Be mobile, engine up those arks then settle down with the industry, you can use the other modules as you please, if the system is appropriate ie temperate for influence cold for science ect. I dont mean to disagree with the above strategy its just well, I do. Does not mean that both can be effective! Just cater everything as much as you can to what you find availabe.