No need to feel pressurized to add a lot of instruments, as in my experience, adding instruments "just because" will tend to just muddy the arrangement. In this ambience jam, I think your minimalistic approach really makes the track shines through.
Regarding the chord hits at 0:29 and reverbs, I found some success using parallel processing for these kinds of situation. Basically you make 2 tracks of the same instrument, set one with no reverb and the other with 100% wet reverb, then you balance the two using the gain/volume mixer. This way you'll have more control over the "main body" of the sound and the reverb as well. Try and see if it works for you.
Great job overall !