Well it looks, to me, like you're going for an "all in one" type tank, which is good. My big tank has a sump and most of my issues have been with sump overflows due to my incredible stupidity and need to tweak things at 11pm just before bed
For example, I adjust the skimmer just a bit, then it overflows everywhere because I'm sleeping and not around the tank. Or not taking the filter sock off the sump inflow quickly enough and water overflows the top of it and down the side of the sump (it used to clog after about a day and a half plus I had a crappy sump design). It wasn't a major problem, and didn't cause any damage, it was just a pain in the butt to clean up.
I have a 5 gallon nano as well (no sump) and I haven't had any problems with it (water wise) and its been running for a year.