To do Returning Armada, after you've researched the ability, you're going to want lots of phase gates (which take up Tactical slots). You can have up to three phase gates on planets and up to two on asteroids. You really need about 15 of them to get RA going.

Doing RA in an online multiplayer game is a much trickier proposition because building the Imperial Labs, doing all of that research, and then building all of the phase gates you're going to need is time consuming and expensive. On a small or medium-sized map you'll get squashed before you can get it up. On a large map with 8 players (4v4) you'd be likely to have a hard time getting RA up. It's possible for a 3v3 on a large single-star map depending on your starting position (buried in the back between two allies. For online multiplayer I only play Vasari on certain types of maps with certain numbers of players because there really isn't any reason to play that race unless you're confident you can get RA up and running. Why? Because Vasari ships are expensive! You might be surprised to see just how inexpensive the TEC ships are in comparison and how quickly you can get a big TEC fleet together. My current default race for online multiplayer is the Advent. (On a small crowded map where I know there's going to be early fighting I go with TEC.)