My turn.
The original question was a general one so I see no problem in posting generalized answers.
Biplanes are not good second planes.
I say that based on the average bipe and average beginner pilot moving to a second plane.
There are exceptions. Some bipes are easier to handle (take the Sig Hog for example) and some pilots moving to a second plane are more skilled than others (either natural ability or longer time spent on their first plane)
I see a number of times that people post that they have many years of flying experience, thats good but how can you judge how well a beginner will adjust to a bipe so soon after learning as it has been so long ago that you were in that position.
I am on my 4th year of flying and have 2 bipes. My first Bipe, an ModelTech SE-5, was my 5th plane and even though it is a gentle flier I would not think I would have been ready for it until about at least my 3rd or 4th plane. My other Bipe is a Great Planes Super Stearman, even though I am comfortable with a number of aerobatic planes including my Showtime 90 I am still intimidated by the Stearman.
My neighbor soloed last year in the early spring, by late summer and 3 planes later he had a 40 size Ultimate Bipe, it lasted about 5 or 6 flights and ended in a garbage bag.
Bottom line. If you feel confident enough in your ability and get a gentle Bipe then you may be ok but as for me I don't think I was ready for a Bipe as my second plane.