Now would be a good time to book; the later you leave it the more expensive it will be. Also such a destination is hugely popular with families anyway and that is reflected in the cost.
Your 13 year old will be paying adult price for both airfares and theme park tickets. Choose direct flights; you do not want same day internal transfers through another US airport due to potential time constraints to reach your next flight.
It will be very hot and humid in Orlando in the summer time; also heavy but brief thunderstorms can occur daily.
I would consider a villa re accommodation.
The Dibb is an excellent resource to look at online.
I would go back to your chosen accommodation and relax post park visit; those places can be pretty full on in terms of walking around. WDW as an entire area is larger than Greater Manchester.
We went to the Flight Centre last June and she told us to come back in September as flights are cheaper. So we did. Direct flights are ££££ more! We do 2 part flights, we tended to stop in Philadelphia which was only 1 and 1/2 hours wait before connecting flights (just long enough for some food) it saved us 2k. This year we are going again but stopping in NY for 5 nights first, Orlando for 2 weeks and then down to the keys for 5 nights. In total with all hotels, flights ( 6 flight) it has cost 6 1/2k for 4 adults (children are classed as adult as older). We stay on International drive and stay in a lovely aparthotel which has 3 bedrooms, free transfers to parks and close to the aqua park.
if you are looking for this summer then you had really better get on with it. we always book a villa and the best one we had was at sunset lakes because it was really near to drive there but not so near that you felt completely disneyfied the whole time.
I would suggest you buy 2 books WDW with kids and Beyond WDW with kids. they are the best travel guides we have ever had and are perfect at answering all of your questions. we book the flight separately through skyscanner and always remember to delete your cookies.
there is evening entertainment at Disney and to be honest my family are of the "first in last out" variety so when we got home all we wanted to do was either flop in the pool and eat or go to bed.