someone will answer me whether it is worth building on Adalon if the base will consist of 20-30 000 people? What will be the speed ?
Technically Adalo works, though there could be some performance impact if the data & relationships across tables are many.
You could offset that storing data in external collections (ex: xano) except for the users (for login).
Same as @bhanu, I would go for now with XANO, I just posted similar answer in another thread. What worriesfor me now in Adalo Collections are the Error 429 (rate limit). I would not want that for a heavy user app until they solve it.