Most, if not all, harpists play the ornaments as published, the appoggiaturas beginning before the beat. This is not correct to Spohr’s period. Music publishers in the 19th century are notorious for changing the ornaments or writing them incorrectly. The on-the-beat ornament is far more expressive, which is its purpose. The turns in the fast passages can be played 1232, which flows into the following notes without repeating the first note which you would be doing if you played 21231, and that doesn’t flow.
To practice ornaments, play a series of them slowly, many times and/or up and down the harp, then play them as part of the line. They must be very clear, very facile, and very melodic as well as rhythmic. The trills definitely must start on the upper auxiliary, in my opinion, and that way they finish rhythmically and lead right into the following melody. I mostly play them as 64th notes, is that hemi-demi-semi-quavers? I have yet to hear another harpist play this piece with “correct” ornamentation. It is not romantic music, it is very classical, just like a Mozart Fantaisie or earlier composers. Spohr was not a radical composer. I have done a lot of study of ornamentation.