Have done Oshkosh from the UK for past 11 years - I did a couple of organised tours then decided it was easier to do it myself.
Have tried LHR - ORD a few time with flights to either Green Bay or Appleton (mainly on United as American did not fly to Appleton until this year)
For the past couple of years I have used Delta to Detroit and again either Appleton / Green Bay. Tend to stay in Appleton as its a shortish drive.
For the show itself it is worth getting there for the weekend before as you should see some of the mass arrivals - 80 Bonanza's is impressive.
Join EAA as if you are staying for the week you get a discount on the entrance fee. It is well organised with 'trams' running through the ground to get around the airfield but you will do a bit of walking. There are plenty of food / drink places as you would expect. Food choice / quality has improved over the years.
Aircraft are grouped into themed areas - Warbirds / vintage / homebuilts / ultralights (they have their own grass runway) with a lot of aircraft parking areas (approx. 3,000 aircraft on the ground this year) There is a flying display each afternoon with a variety of acts that do repeat during the week.
There is also the EAA museum which is worth a visit but does get busy if the weather turns rainy. The seaplane base is worth a visit as you get a number of floatplanes there and it is a less hectic that the main show areas. Buses take you there from the main show for a small fee - 3 dollars this year
The main warbird show is usually on the Friday but warbirds for feature in the other day's flying displays.
If you like photography then that is usually no problem. Few barriers around aircraft although tents etc do sometimes get in the way in the camping areas (another reason to get there early) The east / west runway is good in the mornings as sun is behind. The main north / south runway is good in the afternoons for the flying displays etc. The variety of aircraft that get to the show is its major attraction - this year there were 2 x B29 in formation, B1, B2,B52 in formation (sort of) 12x B25, Blue Angels, F22, F35 and many more. Anyone who has any interest in aviation should do it once as there is nothing else like it.