Considering selling nx500 and lenses?

I agree with Ben, I've sold cameras and gotten something that I thought would be better only to find there was something I didn't care for or that my old gear did better.  Usually it's interface stuff that you don't really get a feel for in reviews or specs, but once it's in your hands you find out.  If you can swing it, maybe buy the new camera and use it for a while before selling off your NX500.  I have never regretted having more than one or two cameras around.  I have actually ended up re-buying camera models that I previously sold because the new stuff had quirks I couldn't reconcile with.

For example...I had a sony A-mount system, sold it in favor a Nex-5t and I wanted to use the aftermarket Sigma lens, turned out that the sigma lens caused a delay in starting up of about 6-8 seconds, so while I'm watching these moments fleet by my camera is slowly waking from it's slumber.  That wasn't in any spec, the only time I saw any mention of it is when I was searching specifically for information on the issue and apparently it's pretty common and not an issue for most folks, but since I have little kids that move quickly and often do cute stuff that the grandparents want to see for about 5 seconds and then they run off, it wasn't working for me at all.  I wasted a lot of money only to go back to what worked for me.

I think Ben offered you some solid advice, and he's an internationally renowned camera slut (since 2002), so I think that qualifies him as an authority in this matter.