I've struggled with the quiver question too, since getting back into sailing only a couple of months ago.
I weigh 85kgs (88kg the other night after a big dinner

) and ride a 93ltr FSW on Botany Bay (with a view to open ocean sailing when I build my confidence, fitness and skills back up).
I started with a 5.9, which I found is good for between 16-20kts. I took the 5.9 out in 25kts and was hanging on for dear life, so purchased a 5.4.
The 5.4 is good between 20-25kts, but again, I found myself struggling in gusts over 25kts, so I bought a 4.9 last weekend.
I haven't used the 4.9 yet, but I'm hoping it will be good for 25-30kts.
That pretty much covers the whole wind range for me. I'm not interested in anything less than 16kts and I can't justify a sail for use in >30kts because it would only get used a couple of times a year.
If you're learning, I reckon you'd be right with say a 5.0, 5.8 and a 6.5 or 7.0. It should cover you from 12kts - 25kts.