How long ?

Took me about 40-50 sessions to get the gybe down well with confidence. That's one whole season where I live. Freeride and wave sails seem to have about a 5-7 MPH range to them before you have to come in and change out the sail size again. Depending on the sail shape some may get more range. For example, I have 3 sails, and they get me out from 12 to about 30 MPH winds. I have a 5.3, 6.0 and a 6.8 sail. I seem to have the best range in my 6.8 and 5.3 sail. My 6.0 has a lot less range due to Its shape.

I was told that you need nearly every size increment lol

Windsurfing is a lot harder to master than Kitesurfing.
And arguably more rewarding.
With your skill set it would be easier.
As to how long it will take to handle waves is hard to say.
If your young and fit and have help and get on the water two days a week , Mabee one year.
If your old and fat like me , only small waves.
Im happy to go blasting too fast in heavy chop , that's more than enough for this old duck.

The carve gybe is basically a surf maneuver. If you're a good surfer you will nail it within a season. In the waves you need to tack anyway.

I once taught a young surfer, he was carve gybing in his first season, and had broken an old board learning to jump. I taught him the quick hard way, bypassed the huge board uphaul bit. And started him off on a light wind wave board, first lesson was how to waterstart on the coming back to shore tack.
But I think he was a "natural", so I guess it all depends on your own ability and dedication, and who is teaching you.
Learning the short hard way is not intuitive, try it without some sort of instruction and you'll give up out of frustration.

I basically use 2 sails (a 5.3 and a 4.7) and 2 boards in the waves, a floaty for sub 15kts and a semi sinker for >15kts.
But I spend more time on the estuary these days, and I use 6 sails and 5 boards for the GTC divisions. This covers 10kts to 40kts, with sails and boards close together to optimise, results for the 6 divisions we compete under.

So it all depends what you want to do, and how often you want to get in the water.

Surfsailing, totally depends if you can really surf and understand the waves.
I know several guys who surf sailed at Ocean Beach, San Francisco, within a week of their beginner windsurfing lessons. Surf was small, maybe head high, winds cross onshore, maybe 12-20mph, beachbreak.
But those guys surfed at the expert level, had surfed there at least 1,000 days, and understood what it took to get a 95 liter board out thru the waves using a 5.5 sized sail.
Everyone learns at a different rate, which has no bearing on the final outcome.

If you kite on a board rather than a twin tip, then you will have some idea on what a windsurfer feels like. Once you learn the basic skills: uphaul, waterstart and planning in the straps and harness, your on your way. There are two schools of thought of how you get to this point, learning on either big or small gear. I'd have some lessons on some big gear (50 litres more than your body weight) to get used to getting going, manoeuvring the board with a sail in 10 to 15 kts and getting on the plane in the harness & footstraps. Once you have successfully planned in the straps and harness, I'd then try a board with volume 10 to 20 litre more than your body weight, find some knee to mid thigh deep flatish water and consistent 15kt breeze and have a go. The niceties like planning gybes, high wind sailing, waves etc will come with practice and time on water. A couple of years ago a good wave SUP rider went to Maui with some windsurfing mates for 2 weeks and was happily planning back and forth at Spreaksville by the end of the trip, so it can be done if you have the right sailing conditions, persistence and time.

Looking at the online tutorials with the big board and small sail make the learning curve seem much easier than what my mate described when he learnt. I'll go get a few lessons when I get home

No I"m not.
Several of my surfing friends were riding 9'6" x 22.5" poly glass boards by their 3rd day total, and didn't have any problems tacking it and a few of the smaller guys could actually jibe 50% within the first week.
Almost all of them could jibe 9' boards within one month, and all tried surfsailing within 3 weeks of their initial windsurfing lesson, on boards around 9' long and 90 liters.
Surfer's are different than most normal folk. We learned to ride 5'6" x 19" twin fins, could stand up on a boogie board on a wave, and the thought of actually using a 9' 90 liter windsurf board is an assault on our senses.
One of my friends was making quad duck jibes at Lake Lopez in the water with George Greenough within 3 months of windsurfing. I could only do doubles my second season, and not a very high percentage.

I could only imagine going down the line would be a vibe over vision thing
But hey I'm plenty alcohol speaking now
Ill shut up now
Bed time