Since your plan is to do some gigging, I'd suggest the 500, definitely. The price increment is modest, and the increase in power will at the minimum give you some headroom. IOW, the 500 buys you some room to grow in your requirements.
If I pay attention to it I can hear the fan in my practice room when I'm not playing. It's never been troublesome when I'm actually practicing! And that's at modest levels--like 80 dB.
And there's no more fan noise than other amps I've owned. Of course, it's a total non-issue when rehearsing or playing out.
+1 The 350 and 500 sound identical at low volumes, while the 500 has noticeably more headroom (stays cleaner, a bit louder, more open low end when cranked). No downside to the 500 other than a bit larger footprint and a bit higher cost. That being said, the 350 cranks pretty nicely, but if you are considering that 8ohm sealed NV15, the 500 would be a must.
I too don't notice any noticeable fan noise with my 350 in my rehearsal space (over other units anyway).
