Is it possible to fly 6 of the same type of ship, for example Y wings? I was unsure if anyone has tried that yet or if it's even legal. If so, has anyone had any success with it?

8 is the hard cap set down by FFG (Tournaments allow no more than 8 ships per squad). Not sure what you're going to get out of 6 bare Grey Squadron Bombers or Crymorah Goons but give it a go if you'd like. Swarms are in an okay place right now.