But is this something I can do with a reasonably flat learning curve?
The short answer is no!
You are right in your thinking
You have 3 options
1 Record
Hire a player and ask them to record the parts you need
2 Audio Loops
These are pre-recorded phrases that can be manipulated in many ways - especially with recent advances in technology
It can take a lot wrangling to get them to recreate what you have in your head - but if you are less fussy then you can go use loops relatively easily to add spice to your tracks
3 - virtual instruments
These tend to fall into 2 categories:
"Synths" that attempt to recreate a sound / instrument
"Samples", which play a short recording of each note
Both options allow you to "play" the instrument via MIDI - either by a keyboard, other MIDI instrument or programming notes with a mouse
The sample libraries can be expensive (and big) because they not only contain a short recording of every note, but every note at different velocities (and or playing styles)
It is then "an art" to play the instrument to get a convincing sound, which is your next challenge!