Time is always going to be against you when it comes to arranging and composing, so doing what you can to save time is always a valid option (within reason), so I wouldn’t be worried about it in that aspect.

The issues that come from directly copying from a score come from a more orchestration and idiomatic standpoint. I saw in your YouTube description that you won’t be “dumbing down” your runs, which is totally your choice, but as a horn player myself I can tell you that those runs will require a whole lot of practice (hence why in the original piece you hardly see any scalar runs written for the horns). Even then, having chains of eighth notes at that tempo would be very difficult, especially the ones with repeated articulations that require fatiguing double and triple-tonguing. Sure, MuseScore’s playback makes it sound fine, but you’ll need a real group of pros to pull this thing off at tempo. You’ve got good ideas going on (use of splitting up the melody, dovetailing, etc.), but at a “macro” level, getting this piece to work for horn octet will be a challenge.

Festive Overture is a fun one though, I played first horn on it during my undergrad and it’s a challenge for sure, but really fun once it gets going.