Hi Ah_ly,
There are multiple questions in your post, not sure this post is the most relevant place to ask them (I’m sure you can find the answers by searching the forum) but here are some answers
Yes, that can be done by using the “autocomplete” appearance setting on your question, more information here: https://blog.cartong.org/2019/12/10/advanced-xls-forms-coding-n3/
You can do it using cascading lists (https://support.kobotoolbox.org/en/articles/592422-adding-cascading-select-questions)
All the best,
Maeve