I'd assume the ingame chat by pressing 't'
It brought up a chat bar that wouldn't go away (I would like it to)
I typed in a few things and Seilore couldn't see what I wrote there. The steam chat worked, but was very difficult.
I do enjoy the multiplayer and I can see the gameflow being slow for this type of game. But pacing is a difficulty for multiplayer (not asking for balance, just a little more speed) I can envision ship battles as being an important side to play with in this type of game, thus a quick way to produce ships may be a boon for multiplayer, provide more ship-ship battles.
I don't know what options you will have for future multiplayer games, but may I suggest when setting up games that we have options that move research well into its later tiers (a quick start so to speak)
A random option where you start with 3 stars and 5 planets would make for a quicker medium / large sized game. That way people still can explore, but have a good base of planets to start building ships and other things with. If that is not possible, maybe settings to decide how many starting ships with which to start the game. Allowing a slider to change the number of colony ships / scouts / survey ships, in the games set-up. (Those would also be good single player ideas when forming a game)
I was surprised how interesting and fun multiplayer is with this game. I REALLY like the fact that I could manage my planets as the other player took their turn. I would set up the initial things then end my turn immediately, and proceed to update, quick-build and set up my planet management during their turn. Gave me something to do while they were considering and doing their turn.