I have a similar background of you. I windsurf up to 1984 in a Carrera and D2. Then 10 years ago ( with 100 kg ) return to ws. First I buy a free ride board 140 lts and a lot of sails from 5 to 9,5. After 5 years of this with a lot of no ws days in the beach I buy my first Formula Board ( a Bic FV1.2). That is the best for Us the old and big guys.
Go Formula with 2 sails 1 x 7.5 mts for the begining and one 10 mts or + ( you will be using 10 mts or more in a few months). Look for something no older than 3 years and fit a nose pad in the nose of the board.
Today I have one board, one sail, one mast and one boom. All the rest was sold.
With a formula and 11 mts sail, you can easily plane ( with 100 to 110 kg) from 8-9 knots to 18 knots in the easy way. And from 8 to 25 if you have a little more experience.