Jabhat al Shamiya is one of the more complicated rebel factions, and has gone through multiple mergers and splits. It initially formed in December 2014 as a unification of Aleppo’s larger moderate Islamist brigades, around a core of Liwa Tawhid remnants. The unification/alliance dissolved within a few months, but that ex-Liwa Tawhid core kept the name, and the alliance lived on as a less-integrated operations room under the same name. The operations room groups later joined the larger Fatah Halab operations room, which incorporated most of Aleppo’s smaller FSA units as well. This left that ex-Tawhid core as the only original Jabhat al-Shamiya member that really kept the name, until Thuwar al-Sham, a splinter group from Jaysh al Mujahideen, fully merged into Jabhat al Shamiya in January. According to Lister’s estimates, Jabhat al Shamiya now fields something like 3500 fighters, but they’ve been split into two wings by the government’s February offensive. Units now in the Azaz pocket operate under the new Mare’ Operations Room, while the units in Aleppo city and its western and southern countryside still operate under Fatah Halab. Jabhat al Shamiya apparently passed the CIA’s vetting criteria, receiving TOW missiles in late January this year, as did several other moderate Islamist factions, namely Thuwar al-Sham and Faylaq al-Sham.
As to your second question, my list is split between multiple fronts and theaters, and divides Jaysh al Islam’s total strength between the north (Hama, Idlib, Aleppo, Latakia), Damascus and its suburbs and the south (Deraa, Quneitra). Lister puts their total strength at 12500, while Alloush himself put their total strength at 10000 in Eastern Ghouta and Damascus, and 7000 elsewhere in the country. I opted for the more conservative total estimate, and given their comparatively sparse social media output, opted for much smaller numbers for Jaysh al Islam’s northern and southern wings. In Damascus, I gave them 12000 fighters, while giving them 250 for both the northern and southern branches. This is all rather rough, of course, but I tried to air on the side of caution.