Yeah, I rarely find people with voice comms, and even then they are usually in a party with other people and chat through an external program so don't tend to say much in game.
Dota is certainly an acquired taste, and don't be afraid to mute people (drop the score board down in the top left, there's a mute button somewhere next to each players name). If someone is being toxic just mute, report and keep playing.
And be prepared to spend fat more money than you would ever think you would on a free game. If you're going to be playing lots over the next month and care about cosmetics, consider grabbing the battle pass. There's a load of challenges in there, earning points gets you couriers, random sets, and if you complete the quest lines you can get some fancy sets too.
And then every major you will be waiting for the compendium to release again so you can do it all over!
Edit: I take back pretty much everything I just said about buying the compendium/watching the major. Perfect World have managed to screw it all up #freeyames