I lied, I will offer more information
For a hunt coat, I would 100% buy used. Get a fabric tape measure, take measurements of yourself, and get a general idea of what size you need. Do not be afraid of buying a coat with too long of sleeves, or maybe a bit too big through the body. No matter if you buy a used or new hunt coat, you will need to get it altered at a tailor so that it fits your body well. When you bring it to a tailor, make sure you get it pinned to fit in your riding position, so pretend that you are holding reins with your shoulders in proper position.
I prefer traditional colors for hunt coats, I would stick with black or dark grey if you are using it for multiple rings.
As for shirts, you can look into 'dickies'. I'm not sure how common they are anymore, but they are almost like bibs for babies and are about $30/dickie. You can get several neutral colors, like white, beige, pastels, etc, and change your color up for different classes/shows. As long as they are neutral and not distracting, it brings a bit of 'fun' to the hunter ring. Plus, if you happen to get one dirty or stained, it is much easier to quick switch than a full shirt. And, they help keep you a bit cooler by wearing less.
However, I would get one, plain full sleeved white show shirt. If there is ever a coat-call due to whether and you don't have to wear your hunt coat, this is what you would wear instead.
For breeches, same thing, get your measurements with a fabric tape measure. You will want light beige show breeches, again, very traditional. If you were showing in one ring, you could probably branch out a bit, but if you are using them in multiple rings, traditional will be best. I used to have a single pair of only-at-shows breeches, but now I use my everyday breeches in the show-ring. It is hard to give breeches recommendations, as certain brands can fit different from person to person.