1) How is the access to water/ice / bathhouses situation?
Showers are at a couple of places in the GAC. Water is available at the showers. Ice is available at the camp store (only one).
2) Do they normally put general-aviation aircraft at the North 40 ? (I have no special status, e.g. not homebuilt or warbird)
There are two GAC camping areas. The traditional one is the "North 40." The other is the new "South 40" or as we call it in Vintage "Green Acres" which is down at the end of the current VAC area. There's another set of showers and camp store there.
3) there doesn't seem to be any way to "reserve" spot at GAC, they said first-come first served; so.... What happens if I do the FISK arrival, land at Oshkos and they say "sorry we are full go somewhere else" _then_ what do I do ?????
Yep, first come/first serve. No reservations. GAC will close from time to time, sometimes because it is actually full and sometimes because they've just not figured out where the empty spots are. The goal of the EAA is "no one turned away" so the camping space continues to increase. What you do is go to some other airport like Fond Du Lac and camp there and take the bus up.
Note that if the taxiways get congested or something bad happens (crash or other incident on the field). The field will close and you'll be told to go elsewhere.
Would they tell me "sorry no room" in the air before landing? or what?
Should be on the ATIS. Certainly you'll know when you get to Fisk.
5) _if_ i fly-in (a big "if") can I get AvGas top-up when there? I could fly it non-stop but would it be prudent for me to land somewhere ~ 1 hour outside of OSH and top-up tanks so I land with mostly-full fuel ?
There are fuel trucks that roam the field continuously during the show. Best to get it taken care of as soon as you get there as it can take a while to get a truck out to you. Fuel prices are not the worst at Oshkosh but not the best either. I'd get on 100LL.COM or the like and find a place not too far away and come in nearly fully fueled.
6) how is departing on Thursday/Friday morning (or any other day) if I want to fly-out? I didn't see anything obvious on EAA's website about how this is handled, I assume the site is closed some hours for airshows but otherwise I can ask nicely to be let-out ???
The only time departures are really a zoo is right after the afternoon airshow. The field closes down for the airshow and there is ABSOLUTELY POSITIVELY NO WAY you are even starting your aircraft at that point in time. There are also times when the taxiways become inaccessible (more a problem on 18/36 coming out of Vintage/South40). This means although the airshow starts at 2PM or whatever, you might get stuck if there's a "demo" going on that keeps us from putting people the N/S taxiways.
If you want to leave before the airshow and you are down south, I'd plan on getting no later than right after lunch.