Yes, swagelok double ferrules design use the same ferrules, materials can be stainless steel, brass, or nylon.
There are Tylok, Hamlet, A-lok(parker), and some others make the same ferrules, since the swagelok double ferrules pattern right has long expired.
Avoid gyrolok, it is double ferrules, made by HOKE, but the ferrule angle is different from swagelok and others.
you can use the single ferrule adapters also, if the ferrule port connect to the tube.(not single ferrule on a double ferrules port)
second question is easy to answer, same installation(same turn) for double ferrules fittings/adapters. But I always hand tight, then wrench turn a little bit, once feel the resistance(ferrules brace the tube), then 1/4 of wrench turn(ferrules press in the tube), because 1 1/4 turn is guarantee for 5000 psi application, we don't have that much pressure in the tube and 1 1/4 of turn is too much. Tighten too much, later on there is no more space for unscrew and re-tighten.
---you can unscrew the nut and remove the components, but the ferrules are pressed in on the tube, can't be removed. re-tighten you need to hand tight then 1/8-1/4 of a turn, wrench tight. Each time do the same, until there is no more space to re-tighten.
The CO2 flow in our application is really a SLOW flow, we have to use any metering valve(needle valve) at under 1-2 turn range.
so a low flow metering valve is easier to adjust the bubble rate.
some metering valves are small CV but not as precise as other same CV metering valve at low turn range. Example, the high pressure metering valves, small CV at full open but at low turn is not as precise as regular low flow metering valve, because the orifice/stem angle is big.
and the Below valve you just bought, is not as precise as other low flow metering valves(same CV at full open) at low turn, but it will get the job done.
And you have a $250(when new) below valve for your bubble rate control.