Welcome to Flyertalk ClareM and welcome to the BA forum. I wouldn't get too concerned about finding out these details from call centres, they get a lot of calls from people asking sometimes very detailed questions, and yet the people answering may have never stepped on an aircraft in their life. On the other hand this forum is filled with people who fly, sometimes many times a week. So for some sorts of questions this really is the right place to visit.

And it is basically a yes to all those questions, you can check-in online (and I would certainly advise it) and via the App with Avios bookings. You should get seat selection, but if the flight is full the options may be limited. However at the airport Aer Lingus staff will be on hand to help get you a better seat if necessary. You do get the same meal and baggage allowance as the rest of the people in your cabin. You are on a ticket like everyone else, there aren't many differences with redemption bookings on the whole.