Best custom race map I have ever played, and trust me, I have played majority, if not all of them.
Here are some of my suggestions:
NAGA
1. Turtle Caravan has 25 less health than Giant Turtle and also is Mechanical (makes no sense, only if it is some kind of game limitation)
2. Naga Tidemisstresses' ultimate Eye of the Storm was not dealing any damage to units. The lightning would struck the ground, but they wouldn't take any damage.
NERUBIAN
1. Nerubian Flyer's fire spitting attack is kind of stupid. I have read here your logic behind it, but still, I am not sold on it. There are like 10 different flying Venomspitters and one random Flamespitter and you have still decided to use fire based attack. Also, name is kind of too generic. Like if Chimaera was called Night Elf Flyer.
2. I would add something extra to Arachnathids. Maybe an upgrade so they are able to attack building while underground or ability to use Poison Stinger while underground.
3. If I queued to research all 3 traps at the same time, the game would let me do it.
4. I would make Swarmer's critters uncontrolable. Free units are always scary. I am sure if thoroughly tested people would be able to abuse it somehow.
5. I would make Brood Guardian's Chitin Shield cost mana. Ability is pretty strong with only 20 seconds downtime. There is little to no skill expression connected to that skill at the moment. It is just "fire and forget" skill majority of the times.
6. I would change Spiderlord's attack while not burrowed to Siege. First, it fits it's theme perfectly, second you are only having 1 siege unit as Nerubian and third, at the moment, roles of Spiderlord and Brood Guardian are a little bit overlapping. Also, I would add Spiked Carpace upgrade to it while burrowed. Just because of those spikes animation it currenlty has.
7. Kind of strange that Everfrost Ziggurat is not having Frost attack.
8. Widow's Deadly Venom should also add poison attack to the target. It is a venom after all, and it is kind of boring ability at the moment.
9. Webspinner's Entomb Corpse has -20 mana cost. I was hoping it would restore 20 mana when you use it, but nothing happened. Maybe is bugged, if not, it would be much needed addition to that spell. I respect the lore-friendliness, but it needs something extra.
10. I would change colors of Gatekeeper. That red really doesn't fit Nerubian's aesthetics. Also his ultimate summons needs another model. They have the same ones are Arachnathids while in the description is written "scarabs".
11. Prophet of the Unseen is kind of boring hero design. Ultimate is the only cool thing about it. I have read that you wanted to have a hero with dispel magic, but she needs something more to make her more stand out.
NEUTRAL
1. When I used Windlord's Airborn ability, Forest Troll was dealing no damage to the hero for the duration.
Regarding voices. I can see a lot of people using AI today to make unique voices for the heroes. I am not sure is that possible for you or not, but if not, why not use fitting voices from other games? Like what you did for Naga Overseer where you have used DOTA 2's Slardar voice. Or, at least, my suggestion is, not to use same voices in the same race. There are like 3-4 different Nerubian units using Crypt Fiend's voice or Naga unit's using Naga Siren's voice. I know they fit those models the most, but sometimes gameplay is more important.
Looking forward for future updates. I am sad to hear that you have only decied to make 3 custom races, but I respect the decision. Kind of curious what is gonna be the last one. Thinking between Burning Legion, Broken Draenei, Fel Orcs and Goblins. My money is on Burning Legion, but we will see.