I reside on MANY artsites. In my experience on all of them, Newgrounds is a Middle tier Art site. Firstly, because you mentioned NSFW, please be wary that NSFW filters do NOT apply to artists' profile/Gallery. It only applies to the Search Areas on the site. If I have my settings to view only up to teen, I can still see your higher rated content if I go to your gallery. Make sure you are Okay with that knowledge.
On Commenting, this website is not set up for Commenting, but critiquing, and thus comments from here are few and far between unlike FA/DA/Weasyl which are focused more around general commenting with your audience. If you are looking for fun conversations with your audience on your art, this isn't the site for that.
I have not delved into commissions from this website as I am stable by getting commissions via FA and DA still, so I cannot comment about commissions on here. It does seem to have a robust commissions area compared to other Mid and lower-tier artsites where commissions are near impossible to get.
On Reaching new Eyes: This site is very slow for me to reach new people. I am a SFW and Gore artist, and also an art-interacts-with-viewer artist, and that is not the type of art that seems to be effective in this particular community. My community on this site is growing, but so slowly. My pixiv is growing faster than my Newgrounds that I started only a few months ago, and Pixiv is what I would consider a bottom tier art site. This website also seems to prefer certain styles a lot.
On DeviantARt: Do you post your artwork into Groups on DA? I post my artwork I want to reach lots of new eyes for into as many groups as I possibly can. DA did just go through a big change, so there will def be a huge activity dip for quite a while. I won't be abandoning DA as it is still a big source of my Income and is still plenty active to reach new eyes. I'm on so many artsites anyways that compaired to all of them, DA is still one of the highest activity artsites around despite the recent exodus.
Back to Newgrounds: I am keeping up on my Newgrounds going on two years now. I will continue to post here as well. This website does have all the things I like in an artsite other than a robustly active community like fa/da. When asked for Alt sites, I do mention NG to people. I've been considering it a side-main. It is def suited for certain artists more than others community wise.
JeveGreen
As long as you tag your stuff properly, you can post anything within reason here. Newgrounds is pretty chill artwise, although multiple pictures in one submission will compress all but the first image, so keep that in mind if you do a set.
If you're looking for attention though, Newgrounds probably isn't the best place to go. It's a bit niche these days. You might get some critique from a passing peep with nothing else to do, but probably not a lot of views. So keep that in mind.
FunkyS0da
Yeah, I noticed that one someone else art work. I'll probably just post things separately. Regardless of whether or not I get people's attention to my work, I do like the atmosphere here so far and I'll probably stick around for a while.