As far as the bipe as a third. Absolutely but not the ultimate. it is a very hot flier to be sure.
Sig Hog as mentioned, my first bipe was a 40 size SE5. Both of these are pretty tame. I would imagine some of the other ww2 bipes would be easier to handle than a more aerobatic model. Just to get used to flying a bipe.
NOW, aerobatic planes as a third plane? That depends on how comfortable with your second plane you are.
SIG Somthing Extra maybe? Super Sportster?
I am flying a Showtime right now and am loving it but I would be hesitant to recommend it as a 3rd plane not knowing your skill level.