For those who are wondering, the good T-dolls featured in this comic (besides the main cast of unique M-16 and M-4 variants) are Skorpion (good off-tank with nice grenade skill) and to a lesser extent STG-44, who is basically not great, but passable. PPSh-41 (Papasha) is not good at all, along with all the AR's that synergize with her, and the "upgrade" version of PPSh-43, Micro-Uzi also is not good. The AR's that go with PPSh-41 (and Micro-Uzi) are AK-47, L85A1, and G3. All of these Assault Rifles suck, although of them all L85A1 is the worst.
The early game is really easy, so don't get fooled by it into thinking that lesser teams are viable long run. By the later chapters, if you commit to a team of sucky T-dolls, you'll be hurting and really regretting it. One of the most popular newbie guides on Reddit says that any team will do and it's most important to get any team to level 100. That guide is WRONG. It was written back when the newest content like Chapter 7 and 5-N weren't out yet, and the harder events weren't coming down the pipeline.
You don't need top level min-maxed teams, but at least use dolls that are "Tier 2" or "Recommended" or at least even more general use friendly "Niche" dolls rather than ones which flat out suck. Also, until you get past the 30's or so, swapping in new T-dolls is easy due to EXP sims and Combat Reports, so don't believe that tidbit about just getting any random group to 100 ASAP. It's better to wait a little and get the right team to max or near-max level than rush to level up a group of weak, throwaway dolls you'll regret using.
I recommend 1 AR / SMG main Echelon and 1 RF / HG (with 1 SMG tank early on because HG's are terrible tanks until around level 80 ) backup Echelon to start with, and to work your way up from there. You don't need to worry about focusing seriously on a Machine Gun / Shotgun Echelon until you reach Chapter 6 or so. While it's certainly worth trying for 1 Shotgun roll a week in Heavy Production once you've unlocked Heavy Production, you won't NEED a MG / SG Echelon until you reach Chapter 5-N, the most challenging content in EN GFL at the time of this writing.
If you need more info, check out the Girls Frontline Reddit, which has links on the sidebar to almost every other resource you'll want / need. Google will also help a bit.