IMHO, if that is the direction you want to go, you are going to have to spend some dollas (“r” omitted on purpose, I just can’t help myself).
Kontakt is a must and, if you are going to get that, you might want to look at Komplete. Kontakt opens you up to a large number of third party libraries that you can add as you can afford them.
I would then look at the first of the Albion libraries from Spitfire Audio. Symphobia from Project Sam is excellent but quite a bit more expensive.
If you want to do that medieval thing, then Era Medieval Legends from Best Service is a must. Forest Kingdom is also good, but I would go for Era first if the video is an indication of the direction you want to go.
There are demos for all of these and I have used all of the successfully in Reaper. I am on the current version of Reaper. My primary is Sonar (I just know it better) but I fire up Reaper from time to time because of its flexible routing and never have a problem with these.
Hopefully, Gareth will stop by here as he is chock full of information on sample libraries. Seriously, his knowledge is massive.
Hope this helps, my friend. Best wishes!