Where to sit is entirely up to the venue and the access allowed, sometimes one can get next to the livestock gates and shoot through the fence, other times you might be limited to the stands. So it is a decision that can only be made by being there and asking.
On the glass I wouldn't be using the 85mm f/1.2 but rather the f/1.8, the AF on the 1.2 is considerably slower than the 1.8. And adding a TC behind it will only add to the limitations by slowing AF more and the lose of another stop.
The 1.2 is a beautiful piece of glass but in no way is it considered a lens for sports photgraphy where the 1.8 is one of the favorite indoor sports pieces of glass for its quick and accurate AF not to mention the great image quality.
But again I would not put an extender on either of the 85mm's. Doing so adds a stop to the glass and only gets the focal length to about 119mm, so for the cost of a stop you are limited to two focal lengths where the 70-200mm f/2.8 has a much larger focal range and is already setting at almost an equivalent stop without the inherent limitations of using a TC.
The 100-400 will probably to slow of an aperture even wide open for an indoor rodeo so I wouldn't be bringing it along.
Also I think the recommended shutter speed of 1/200th is about half of what you will really need to freeze action, consider you need at least 1/400th to capture basketball with high school kids, I can promise a horse or bull can move considerably quicker than those kids do.
As mentioned if you are shooting jpeg set a custom white balance for the venues lighting, it will save a lot of post processing and headache later.
If it were me I would be shooting manual or maybe AV, center AF point, AI Servo, center weighted metering, ISO set to keep my shutter speed above 1/400th, and at the arena floor level if I could, and as mentioned if shooting jpg's a custom WB; these would be my basic settings before a single frame was clicked.
Have fun, good luck and be sure to share some shots.