Specialization Groups

[Lastelli]

You cannot be sure in advance as every new recipe they add may or may not need some materials from a different specialist.
Typically, LTW and WVR rely a lot on each other. Sometimes they also need some gemstones from GSM. Masterbook III recipes are such that CRP and GSM are pretty much self sufficient, while the other crafters (bar CUL and ALC that are always self sufficient if you exclude Grimoires and Codeces) have to rely on different crafters, but I don't think this is a precedent. It may very well be that for the next recipes GSM and CRP will have to ask other crafters for help.
My suggestion would be, pick WVR-LTW or CRP-LTW (for some reasons there's a lot of wood involved in leatherworking) or again ARM-BSM and then add a third specialist of your choice when the next recipes come out.

[LystAP]

My suggestion would be, pick WVR-LTW or CRP-LTW (for some reasons there's a lot of wood involved in leatherworking) or again ARM-BSM and then add a third specialist of your choice when the next recipes come out.

I tried ARM-BSM, but ultimately gave up ARM since both BSM and ARM have a lot of overlap with the other, such as with High Mythrite Ingots. LTW can be integrated with WVR, but also works with GSM, since the former often also requires gems. Of note, if you intend on making money, WVR-LTW specialists are relatively common, and you'll most likely have increase competition (and lower revenue streams) if you should choose that road [depending on server].

ARM-BSM is also relatively common, BSM considering the tools and ARM because of how it integrates fashion/product-wise with WVR-LTW. CRP, GSM and especially CUL specialists are rarer, and could charge relatively higher prices for their products.