Hi Connor,
Karl and Sleep on Latex is a reliable supplier and these are all high quality materials (100% natural Dunlop). You can read more about the different types and blends of latex in post #6 here.
I would also keep in mind that if you haven’t tested the specific combination of layers in person then only your own sleeping experience will be able to tell you for certain whether the layers you are choosing are a good match for you in terms of PPP (see mattress firmness/comfort levels in post #2 here).
It would certainly be all you “need” at your weight and you would need to be closer to the high 200 lb range to “need” more than 9" of latex although a thicker latex mattress may still be a preference for some people. I would wait until you have tested the three layers you’ve ordered before considering any additional layers. There is also more about the benefits of a thicker mattress in post #14 here.
You don’t need a single 6" core no. There is more about using two 3" layers vs a single 6" core in post #2 here.
I would keep in mind that you will also need a good quality cover for your latex layers. Some of the better sources for mattress covers are listed in the component post here.
Phoenix