Re admission: I think you are correct that people arriving Thursday or Friday pay the same rate as people arriving on Wednesday. The fact that people arriving Saturday pay only $10 less than people arriving on Wednesday tends to support this.

Re flying with armor: The only hassle the airline gives you for flying with armor in checked luggage is about the weight. Airlines that used to accept unlimited pieces of luggage weighing up to 75-80 pounds each now limit you to two pieces luggage weighing no more than 50 pounds each. Woe betide he who must pay excess luggage surcharges! They are quite costly!

Warm cloaks (you ARE bringing a warm cloak, aren't you?) are heavy and bulky, so generally I wear my cloak onto the plane. After all, it is indisputably a piece of clothing; there are no rules against wearing medievel outerwear on an airplane nor are there rules requiring you to continue to wear it during the entire flight. In the past, I had good luck duct-taping a shield alongside a suitcase but that was pre-911 and I don't know if the airlines would go for that now. They would probably get frightened by anything that looks weird. You could probably get one of those huge soft-sided suitcases for $5 at Goodwill and stick your shield in it along with other stuff, but again watch the weight. Probably you will need to split up your shield/armor between two suitcases, and stuff the remaining empty spaces with sleeping bag, garb and other lightweight stuff. Also, if you can bring your <heavy> helm as a carry-on all the better, even if you have to stick it in a backpack or small duffle bag to avoid the weirdness=fear issue.

With regards to flying with armor as long as it is in checked baggage there is no problem. I fly with my armor and swords all of the time and have never had a problem. When crossing international borders always declare it all to customs though:-)
This is going to be my first Estrella as well. I'm usually active these days in the Kingdom of Lochac.

Regards
Emrys