is there any way to see how many seats are already booked before I book?
no, but you can see the seat map, so you can see the available seats at the time you look at the map
go to US Airways US page, choose "book flights", enter your itinerary and dates
on the result page you'll see a "seats" button in the travel time column
this will allow you to see the available seats at THAT time
but remember that seats assignments are not guaranteed.
Once you've booked, check often, because sometimes they merge flights and someone in your party gets bumped a few rows back. Happened to me a few weeks ago, but we eventually all got reconnected together 3 rows behind our original location, mind you we're on row 14, front part of the wing section.
as long as you book early enough (we booked 8 months out) you should be ok
Plus I am looking at flight round about Easter next year so I presume this will be a very busy time?
a busy or a slow time does not exist anymore
your flight will be booked solid wether you fly in october or for Easter.
Also those that have flown with them, how did you find it?
prettuy good.
Flight attendants were very nice, food was ok (smaller portions than on other airlines but they won't let you starve to death

)
very nice selection of in flight movies, shows, music and games for kids
I have read some horrible reviews about old planes etc and again being a nervous (well more terrified) flyer it makes me dubious to book.
you'll get a A330 for the transatlantic flight. Very nice plane to fly in.
You might get an A320 for the domestic flight, or maybe a 737 which are both nice planes
The planes I've flown in with US Airways were all ok
the only time I was "disappointed" with an airline was with United who get you across the atlantic on a 757 which is a close to a sardine can as a plane can get when it comes to transatlantics.
All in all, US Airways is definitely not the worse airline to fly with (and they're cheap)