Hi Wey, you are getting lots of stuff lately!
Galaxies end up being an obsession to most of us. Regarding M83, that bright star in the middle sounds like it's the core. Most galaxies are very faint, if you are observing from a dark site you're more likely to see some sort of spiral structure. With M83, I've had no luck from my suburban backyard seeing an structure, I can only see the core. Most of the viewable galaxies are elliptical so they just fuzzy dots really - some brighter and bigger than others - so observing spirals is such a treat.
I've found that using too high a magnification makes the views worse as yes, higher mag does darken the sky background but it also dims the galaxy. M104 The Sombrero Galaxy is one of the few that can take high magnification well because it's quite bright. I found a 7mm eyepiece hits the spot nicely with it. I generally observe galaxies with either my 15mm or 10mm eyepiece.
If Saturn looks super, up the magnification!!! Don't be afraid to go for a 5mm eyepiece. If it looks good in that, up it even more.
It sounds very much like M8 the Lagoon nebula that you got
.
As for the globs, I have a widefield 10mm eyepiece and that's generally what I use to observe them in as it fits the entire glob within the field of view very nicely
. Having said that, a 15mm gives brilliant views as well.