RE: Minimum sail size for Formula Exp 160
Given your weight (74kg), I would recommend a 10.0, sail with cambers. In the beginning, you may not plane in 7-9 knots, unless you have good pumping skills.
Get a formula carbon boom, that will fit sails from 8.5 to 11.0, which will take care of your future needs. Add an adjustable outhaul, which will extend the range of the sail.
With the 10.0 sail, you will need a 520cm carbon mast, at least 75% carbon, but preferably 100%.
I am not familiar with North or Severne sails, so someone else will have to jump in.
Combining the mast, sail and boom, you are looking at about $2,100 US for retail prices.
Buy an "Easy Up-Haul" or make one from your uphaul. Advanced formula rarely drop their sails, but if you do, and it is windy, the Easy Up-Haul will save a lot of energy.
It will be worth it - go for it.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.