Ah, if you really need a good/easy to use score view, then I wouldn't recommend Reaper.
The score view is really basic in Reaper, and entering notes in it is really not intuitive, the one in Cubase is a lot better since they recently upgraded it a bit.
But even if the score view pretty good in Cubase, I still like to compose big arrangements like this in notation first, since inputting notes in the Cubase score view has always felt a bit cumbersome when i've tried it.
Cubase and Reaper both have trials, so you could test out the trials to see how they both feel to use for you. Learning a DAW takes time so I would really recommend using the full trial periods to get a feel for both of them.
If you need some other sounds to use with The Orchestra Essentials, and you might already know these, but the free version of the Spitfire BBC Orchestra is pretty good and then there is the FREE ORCHESTRA 1 & 2 by ProjectSAM, Blueprint series by Fracture Sounds and SineFactory series by Orchestral Tools. If you haven't used any of those, I highly recommend taking a look, since there's a lot of good stuff included in them.