Hi Mike. Welcome back to FSX. If you're considering ORBX Scotland then your existing Scotflight scenery is likely to give you problems. Some airfields work perfectly (Kirkwall, Benbecula, Stornoway for example). Others, (Islay, Inverness, Sumburgh) have some issues but.....fear not! As you can see above, Iain is in progress of producing a version of Scotflight that will work with the ORBX scenery.
The ORBX scenery airports are basically all the airfields that are represented in FSX slightly jazzed up and a more detailed Dundee. They are not in any way as accurate reproductions of Scottish Airfields as those in the Scotflight packages.
I actually use and like ORBX Scotland but I don't want to be unable to use Scotflight and will be getting the ORBX compatible Scotflight when it's released. I do have a small criticism of ORBX Scotland and that is that Orkney, Shetland, Harris, Lewis and the Uists have too many trees. However, when I say that, it's not a major issue and there are a few of us who are attempting to get ORBX to carry out some forestry.
A lot of what you decide to do is going to depend on the sort of flying you want to do and how high is your CPU power as many complex add ons will reduce your frame rate and possibly your enjoyment. i have to say I don't find the ORBX or Scotflight scenery hard on my PC However, if you decide to go for, say, UK2000 Edinburgh for a really detailed Edinburgh then that might.
Forgive me if I'm teaching you how to suck eggs here but it isn't a problem to mix your add ons provided they are correctly layered in your 'scenery library' in FSX. For example, ORBX scotland would come below Scotflight but UK2000 Edinburgh would come above Scotflight, (if you decided to go down that route).
I hope this is of some help and I apologise to Iain for mentioning other companies products but as you can see, I wouldn't be without Scotflight!
All the best.
Mike