Greetings Charles,
As a fellow martial artist, my sole recommendation is that you don't consider making an expensive purchase due to pressure, even for tameshigiri, most live blades outside of Japan will render a similar performance. As for blade geometry, not much deviates from common sense, thicker blades can make cutting straw easier, but will enfeeble your batto/notto. Blades with bo-hi produce tachi-kaze (blade wind) with most correct cutting motions, those without it often produce a lesser sound and have different balancing. Some degree of curvature is helpful towards notto, but excessive examples take nuanced handling.
I wish you continuous luck in your efforts, and don't be afraid to ask questions, we get bored without them!