I see you got a hat already, but I was going to suggest just picking up a straw hat with a good shape. They're much less expensive than felt, and you can probably reasonably get away with it in October.
Use a shank bit on your senior horse. Hold the reins in your left (or non-dominant) hand with one finger between the reins. Put your right (or dominant) hand down at your side. My trick for holding the free hand still: grab a couple pieces of chap fringe.
Make sure you know some of the common conventions of the WP show pen: pass on the inside (toward the center), NEVER circle like the hunters often do, and be prepared for reversing at the walk or jog, and being asked to back on the rail.
Quarter Horse bend, or crease, sounds like it should be right! As long as the brim is well-shaped and not flat as a pancake or squished up like a taco (what I call the "Toby Keith fake cowboy hat") you shouldn't look terribly out of place!
Jimmy (a man of many words) is the Show Chairman and he is fine with it.
Jimmy to me
Should be fine.
I was looking at the rules and saw nothing regarding bits for Western Pleasure classes. I know the standard is green horses and 5 years old and under wear snaffles/bosals and 6 and over wear shanks, but this was not mentioned. I have a green 7 year old that will be competing in this first ever WP class this weekend and would like to ride him in a snaffle. Is this permitted?
This sounds like a fairly small local show, right? I highly doubt they are going to be asking for a copy of your horses papers to verify the age if you show in a snaffle. Ride in the snaffle, you will be fine. I've done it before at a small local show with a green mare who didn't neck rein very well yet.
I second the advice to be prepared to show in the shank, just in case. The show management might allow it, but the judge might think differently. Even if he's overruled, you'll be automatically on his bad side if you go against his opinion. May as well give yourself the best possible shot!
We had a blast! I just enjoyed getting to wear the clothes! Plus, I co-own with my boyfriend the mare he was riding, so I'm glad he was the one to beat me. Plus, we got a third! Who cares if it was out of 3