I bought a board+rig package from isthmus last year and only got a few days in the water in September and November. Some of you may have seen me struggling to get anywhere but drifting downwind into the boat ramp area at Greenwood beach
I'm 200 lbs, 6'1
Tahe Beach 185 D - big, heavy rotomolded skin, probably indestructible
RRD XTRA 6.5 sail
430 SDM 70% carbon mast, RRD 34cm extension
I don't see any adult taking anything less than 7 meter sail out on Michigan - some of you are lighter, some probably about the same weight.
I did recently pick up a really nice 100 L board (from the 90's yeah!) a 7.5 cam sail. My neighbor threw his entire 90's slalom race rig over the fence and said have at it

For a 90kg/200lb rider - does that Isthmus starter package sound like the wrong choice?
I don't remember Isthmus asking how much I weighed or what kind of strength I might have. A few surfers at the beach said I might get a ride but definitely not planing. I feel now like an 8 or 9 sail on a wide 100-120 liter board would have been something I could get started on in 10-10-13kt winds.
The 6.5 sail's luff is maxed out on the 430+34cm combo so I have a 460+48cm combo for 7-7.5 sails.

Lol, I had the same issue when I started back in 2010. I also bought a package-in my case a Bic Techno/Core 160D and a 6.5 sail. I could sail back and forth, but I couldn’t plane in the footstraps in the moderate winds and in stronger winds I couldn’t control it with my next to 0 experience. Things started to change for the better when I bought a 7.5 -a cambered Ezzy Infinity 7.5 brand new. With that sail I did my first planing in the footstraps the next year about a mile offshore from the Gary IN beach . Later that same year and with the same kit I almost drowned when I catapulted hard and got entangled in the harness lines, but that’s a story for another time. In about 2 years I had replaced my starter kit completely with a 112L slalom board, 7.5 and 6.5 sails and a 93L freewave board and a 5.7 matching sail. 12 years later only pictures and memories remain from these boards and sails as I have replaced everything all over again.

So, your starter kit is just that-a starter kit for a big guy-complete beginner. From this point you begin to add different sizes sails and boards to match your progress and needs. Start with the bigger sail sizes and when you get comfortable planning in the straps you can start looking for a better board and so on.

Here’s my only picture remaining from that first glorious planning kit

I'd go for 7.5 instead of 6.5, but it is a right beginner package overall. Greenwood is not the best spot for learning since it get's choppy if there is barely any onshore wind and offshore wind is gusty close to the beach. Ideally you'd want to train planning on flat water first - lake Andrea, Silver lake etc, take a trip to OBX... Generally bigger boards of more or less similar shape start planning sooner at lower speed compared to smaller boards, so unless you can get going on 185l there is no point in trying 120l. You won't be able to uphaul on 100l board, it will require waterstart which is hard to do with large sail. You should be able to uphaul on 120l but it will be challenging in swell. Cambered sails are also not very friendly for learning - they are heavier, harder to rig and little harder to flip around when learning how to turn, I'd stick to freeride gear for learning. Also keep in mind that sail size is limited by the fin size you use. My ultimate low wind lake Michigan combo was 161l formula board + 10m sail.

Good advice from Ady and Dimitry. I think that 185 board with retractable dagger is probably the right size given your weight and ability for starting off and learning how to plane. One other thing to keep in mind is that as you get bigger sails, you should have corresponding bigger fins. I see that that your current board comes with a 30 cm stock fin. Check out this Windsurf calculator by Jim Douglass: http://jimbodouglass.blogspot.com/2010/11/updated-windsurf-calculator-online.html

One of the tabs is for sail size and another tab is for fin size. According to this calculator (which I've found to be fairly accurate), for a sailor at your size, 6.5 should work in 21-22 mph winds. If you wanted a lower threshold, the 7.5 should work in about 19 mph. An 8.5 should work in around 16-17, and 9.5 should work in around 15 mph.

As for fins, a 9.5 should be paired with a ~50cm fin, an 8.5 with around a ~45cm fin, and a 7.5 with a ~40cm fin.

So, it seems to me that you have at least two basic options.... 1) if you want to go out in the lightest possible wind and you have the extra cash, consider a 9.5m2 (which would allow for ~15mph winds) or an 8.5 (which would allow for 16-17 mph winds). As some windsurfers are moving more toward wind foiling, you might be able to score a good price on a used 9.5 or 8.5. I've had both. 9.5 is great for lowest wind threshold, but a bit of a bear to handle in sub-planing conditions and considerably challenging to waterstart. The 8.5 freeride will feel a bit lighter in the hands when sub-planing and is slightly easier to waterstart (once you know what you're doing), but requires 1-2 more mph winds to get planing. 2) if you want to keep expenses to a minimum, stick with the 6.5 and 7.5, but know that you'll need at least 17-18 mph winds to get planing with the 7.5. In any case, I would recommend, a bigger fin (~40 cm) for the 7.5 in order to plane. For learning to waterstart, the 6.5 will be the best bet in 21+ winds. If you can get upwind with your centerboard, LM on a flat day will do (even if blowing SW), but if you're still working getting upwind, then I and I agree that an inland lake like Lake Andrea would be a good bet.

Good luck as you continue to progress. That magic day will come when wind speed, conditions, and gear all match up and you'll be skimming over the water before you know it.

You chose good gear to learn on. I weigh over 200 pounds and at our weight anything less than 18 knots is light wind. No matter what gear you're on it's going to be hard to learn planning skills in light wind, but once you've got the skills you can get the gear (if you want) and your light wind threshold will be much lower. Don't be afraid to drive for the right conditions. Wolf is a good place to learn.