Gidday mate,
I made the switch a couple of months ago and will never look back. In terms of reliability (ie: crashing etc) P3D is streaks ahead of FSX. In terms of performance, I wouldn't say that P3D is easier on your system; however what I would say is that for given FPS, the graphical quality is far superior. Like anything though, there is never really a time where you're achieving huge FPS with everything turned up.
In terms of addons, I can't speak for VLC but it appears you've been answered by TopRob. But in regards to others, I have seemed to make most work (either by simply installing through the developers installer, or by manually placing the files in P3D - seems to work).
My current addon list is:
REX 4 Texture Direct
Orbx NZSI, AU, Global
PacSim Rarotonga
Aerosoft Airbus X Extended
Majestic Q400
Most of the Carenado models
RAZBAM Metro III
All of these are working fine

Good luck!