Even if Gilmour would leave, I don't think any more midfielders are coming in. Another CB and/or another RB could come but anything more in terms of midfielders or attackers looks very unlikely to me. The competition is already unreal.
Good. Think he would have struggled for game time. Not sure about letting him stay at the dire level that is MLS but could imagine it was part of the price.
Will be interesting to see how he'll be used. I think he looks a fair bit like Gross - he's fundamentally a creative and attacking player who likes to work hard and take a lot of defensive responsibility. Brings another kind of balance compared to using a player like Joao Pedro or Enciso in a 10...