Sail and Board Sizes For Slalom?

Got my first slalom board a 122 Falcon, 75cm wide, to start doing some slalom racing (recreational)

I have a old 9m Code Red that I can use initially, though the sail is a bit tired, so will probably replace it with an 8.5.

I don't have any other race sails that I could use, (i have wave freestyle gear from 6.3 and down). I would like to end with two slalom boards and three sails. A light wind set up (big board big sail) and two smaller sails to cover 18knots and up. Will probably get a mix of 2nd hand and new gear, and make a few tweaks once I figure out what sizes work best, so looking for some advice to avoid picking the wrong sizes.

I weight 74kg, I am guessing an 8.5 with a 75cm board is as big as I would need to go at my weight? dropping down to a smaller board with two sails for 18+

I prefer to have a closer spacing and comfortable board to cover the 18+ range rather than a more linear spacing. So I was thinking of dropping straight down to 7 or 6.7 and partnering with a smaller sail on a 63 or 60cm board.

Main reason for hesitating on the drop from 8.5 and down is trying to avoid mast sizes I don't need. I need to decide how much I want to drop down from the 8.5.

up to 6.7 a 4.30 will do