A few items not clear to me:
1. Can I purchase the student license or is it $199 for a 50 year old flight simmer?
I purchased the academic license although I am 53. Mind you, I am a permanent student too. It is meant to be a learning tool and I read it that it is OK to use this version as long as you have a genuine desire to learn (as opposed to just "playing").
Its based on honor. If you are a student of flight, you definitely qualify. If you can afford the pro version, and you arent a student, please help out P3D with your pro purchase.
For Developers, we can get it at $10.00 USD a month. Also, if you want to 'demo' the platform to see if it will run on your rig, buy the 'one time, 30 day purchase of the Developer version for $10.00 USD and you can run it for 30 days to see if you like it. I did that and fell in love with the sim. (FSX wouldnt run on my computer, this, P3D, does...).
2. Can I have both fsx and P3 installed?
Yes
I did for a while (although FSX has now bitten the dust).
3. can I load models i have purchased for fsx into P3?
Yes
I have yet to come across any add on that hasn't worked. And I have lot of them. FSX to Prepar3d migration tool is really useful
http://www.flightsim.ee/products/fsx-to-prepar3d-migration-tool
Just make sure that you respect EULAs
4. do I have to uninstall fsx add-ons from fsx before I can install them in P3?
No, not usually, but with some ultra sophisticated addons, you might have to ask the developer team if you can. Usually you can load anything that is for FSX into P3D 'also' as they are the same sim platform. P3D is an advanced version of FSX; same folder system, etc.
Some scenery systems, as like ORBX still slightly are, have DLL's and programs that run scenery, and are delicately installed into specific locations. Some people can put a copy of the FSX.exe program into the main Prepar3D folder and that will fool the installers into loading FSX meant scenery packages into P3D.
Mostly you can leave them in one place and point the respective program at the location. P3D specific programs will have to be installed separately.
Mainly with 'scenery' will you need to do this. You can link in scenery directly from FSX into P3D. But, things like ORBX DLLs and scenery management programs, those need to be 'in' the P3D folder system (the programs) and they need to run 'with' P3D. ORBX was running fine with P3D, but on the latest update to P3D, some DLL's had issues. I am not sure if ORBX have cleared that up yet. Popups come up during P3 bootup concerning 'dll' performance, asking 'do you want to run this or cancel. It asks this 'every time' you boot up the sim. Annoying. Its never done this before.
Hope this helps you to make the jump to P3D. It really is worth it.