WHAT HAPPENS WHEN MULTIPLE PLAYERS WANT THE SAME PLAYER COLOR (DUE TO THE VARIED STARTING RESOURCES)?

In some games there might be a benefit to a particular player color (from scoring scheme, expansion tile, etc). Normally the player order is determined by taking all chosen color pawns and shuffling them down into the tile queue. Instead, players can agree to "draft" the colors: first the player draft order is chosen randomly (die-roll, etc). Then in draft order, each player picks their color and places their claim pawn in the queue next in order behind the starting line. This way, the player who gets first choice of player color would go last in turn order.

When I buy from the Exchange, where do I put the purchased resource token?

Because players can only purchase from the Exchange when they are trying to pay a cost, there is no need to (in fact, you should not) take the associated resource token. Trick question!

When exactly can I sell to the Exchange?

Unlike buying from the Exchange, you can sell to the Exchange at any time during your turn.  This includes before you move your claim pawn, after you place it, or even right before ending your turn.

What happens when I have no options to build any the blueprint tiles showing in the queue?

While this comes up VERY RARELY (theoretically never with decent planning), mistakes happen and this comes up once in a while.  Our solution is to pay 5 points and move one of your astronauts to any tile in your base plan (just like the DRINK action of the Coffee expansion tiles).  That should do enough to find you a place to build.  Note: this rule is not there to be abused, but as an escape valve for newer players.

When does the gap made by POURing the Coffee tile get filled back in?

While the gap is not filled in the current lap, when players continue the game and have all passed the POURed gap, it will filled seamlessly with the normal progression of the game.

Majority/Dominance: when you say "most", what exactly do you mean?

"Most" here means more than each other player.  Not more than all others combined, or anything else: if you have 6 and everyone else has fewer than 6, you have the most.