RE: Carve 131 and 101 or ???
I think that you are spot on with the C101. It is a significantly smaller board than the C131 and would be a nice transition without beeing too demanding.
As such, for a 80 KG user with 5.4 as the biggest sail, it would actually make sense to pick a slightly smaller board, going even towards 90 liters. But these boards do get more challenging to sail, and are maybe the next step in your career.