Hi Mark
Thats a really nice image. I like the colours, very strong and the pillars are pretty cool
The blacks seem clipped around the darker areas towards the top and tweaking star masks might help with some of the smaller stars if you are desperate to lose all of the magenta
On the RGB, give it a go. I wouldn't bother with the L but short RGB subs should be fine if you are just looking for star colour, subject to whatever your gradient removing tool of choice is. The last 2 cluster images I did where taken from a very short bus ride away from the CBD. 3 minutes subs tops, no LP filters, but not sure what that translates to with your ASI1600.
