My friend rides IEA; she says it's a blast. I would love to try it.
My favorite inexpensive but sturdy breeches are Devon-Aire; I have 3 pair, but you have to try on a few different brands and styles to find one that fits you right. Every brand fits different, and you have to see what works best for you. As for show shirts, they do not have to be white. The guidelines are the same as in the hunter ring, so navy striped and sometimes plaid shirts are often seen. I honestly don't have a preferance for show shirts...I have 4 or 5, all different brands, and I don't notice a difference.
Tall boots, navy/black/gray jacket, and for helmets I reccomend a GPA, IRH, or velvet helmet. Troxels look tacky in the hunter ring, IMO.