Japanese Koto uses the Hira Joshi that is minor scale with MI and LA being flat, Chinese guzheng uses mainly the Nogi Joshi (in Japanese koto system) that is pentatonic scale Korean Kayageum is the Korean variant of Koto/ Guzheng.
(the kayageum is close to the Chinese zither but has bridges, and played without picks)
Guqin (zither) is the most ancient form that lacks bridges and the tones is pressed with the left hands and a lot of sliding tones. www.youtube.com/watch?v=6sVIV2…
This is the 3 variants side by side. (Jasmine, Bellflower - Chinese Guzheng pieces) (Sakura Sakura - Japanese Koto piece) (Arirang - Korean Kayageum piece) www.youtube.com/watch?v=3B8xS7…
Japanese Koto are usually 13 strings, while the Chinese 21 strings guzheng is called "nijugen" or "20-string", the 21 strings variant does exists in Japan. the "25-strings koto" is called "Se" in Chinese which isn't as common since most of the pieces are written for 21 strings.
You can make the picks from materials like acrylic, polypropylene (plastic tubs), and even polystyrene (though polystyrene isn't too durable and tend to chip)
These are guzheng picks I made, hand crafted with sandpaper and flower pruning scissors for trimming the pieces into rough shapes, so no power tools needed. the first picture with the black turtle shell set is actually a set made by an artisan friend from Beijing These are Beijing styled picks that is sharp teardrop points, that is close to the Yamada Ryu picks in Japan
Japanese koto picks uses a leather loop or rubber ring, which the Chinese guzheng picks uses bandage tape for sticking the picks to finger,
so if you are making your picks just get a 24mm wide bandage tape and slice it into 3 slices of roughly 8mm strips which will be sufficient, duct tape is sticky but the perspiration will be trapped making it slippery after playing a while.