I mainly play as Falck since I always play as medics in Battlefield games. I use the AC-42 with Champion muscle and either underbarrel frag or smoke grenade, depending on how the match is going. But recently I Discovered it is very fun to play with a Bipod Avancys and extended magazine with the togable sniper scope (I forgot the name of this scope) and play more of a Battlefield 1 LMG style. This can be very helpful for advancing or defending objectives. Sometimes I use the PBX SMG for when I need to run around a lot to heal and revive teammates and then I want more mobility and a lighter weapon. As secondary I also use the G57 for exactly the same reason as you 😛. Weirdly enough I have it completely stock and that feels best.
For gadgets I always carry throwable smoke grenades, the smoke grenade launcher and the ammo box to resupply my team ammo, gadgets and my own smoke grenades. I highly recommend support class players to use smoke grenades when reviving teammates that are far away or near combat. Either to safely revive them or to cover some distance you have to travel to your downed teammate. Use the Smoke grenades for “circular” smoke clouds and the grenade launcher for a “wall” of smoke clouds. Depending on the situation and your own position and that of the enemy you can choose which smokes to use. Use an underbarrel grenade launcher for assault rifles for fragmentations so you have more attack capabilities or even extra smoke grenades. I notice that teammates start advancing to objects in Breakthrough if you drop 3 walls of smoke with the grenade launcher and your normal smoke grenades. But it can also be used defensively if you shoot the smoke far away near the enemy spawn area because they have to get out of cover or you can stall the incoming attack. It is also useful to cover your retreat to the next sector or to cover a friendly vehicle in smoke that is almost destroyed so it can escape. Just dont drop smoke grenades near snipers or CQB players. Let them do their thing so your team can win.
Irish deployable cover works with a bipod and could be handy for LMG players. You sacrifice mobility but you can create a defending spot anywhere on the map for yourself and your squad. Drop some ammo or health crates at your location and spray some bullets towards the enemy. This works well in tight spaces or around corners and you can create safe areas for your team to resupply or heal.