I went from a Kadet Senior to a four star 60 to a Hog Bipe. The four sttar 60 was short lived about 20 flights --my confidence far exceeded my ability. The Hog Bipe was hurriedly completed for service. I had few problems beyond adjusting to the flight characteristics. The LT-40 is a little hotter then the Senior and its a tail dragger. I jumped from the Senior to the Bipe with only limited experience on a low wing trainer and did fine. I would think your jump would be similar to mine. Master the LT-40 completly --complete circut inverted, confident repeated basic aerobatics and you could to it. Get your buddy box out for the first biplane flights. Let an experienced pilot land so you can gauge the different approach pattern. I recommend the Hog Bipe and move the landing gear forward 1/4 to 1/2 inch to improve ground handling.

Consider this: My biggest problem was fear. Fear that I would crash and ruin my plane. I spent about two months with twitchy thumbs because I did not want to lose it. This limits your enjoyment of the hobby. If I was to do it all over I'd still build the bipe as a third plane and get more time on the four star before crashing it.
I all but went from trainer to bipe, one can do it. IMHO get a four star as a second plane you'll enjoy flying it more. Can't enjoy hobby when you fear crashing.