Tomas Slancik

you can play with Attribute Blur SOP after your Connect Adjacent
- in Group set all points except for anchor points
- uncheck Fix Border Points as for Curves all points are border points
- additionally you can control it by weight attrib
- also play with creating your connections, essentialy you probably want the adjacent connections only between lines of the same clusters or something to not have cross webbing

raincole
Set POP Drag's air resistance without wind seems to do nothing

try higher values maybe? It defilinely should apply drag to Vellum Fluid particles

on Vellum Solver SOP you can also use Forces/Built In Wind Drag, which is linked to internal POP Wind, but regardless ow what POP Wind or POP Drag you use you should see the effect

if you render pure emissive volume it will have no Alpha, which is correct and it will also not block any other light

the comp should be simple, just Add over the plate, not sure how it's called in AE, in Nuke is called Plus
Assuming your soft assumes the image is already premultiplied (which it should) you can also use Over, since if Alpha is 0 then over is the same as Plus: A + B(1-alpha) = A + B(1-0) = A + B