Philippine-American Dual Citizen Seeking Spanish Citizenship

Hello everyone!

I am a dual Philippine-US citizen (born in the US to a Filipino mother). I have read that after 2 years of residence in Spain, a Philippine citizen is eligible to apply for Spanish citizenship. I have two questions about this:

(1) If I were to apply/receive Spanish citizenship after 2 years of residence in Spain, what would happen with my Philippine and US citizenship? Would I be able to keep them, or would I have to give up one or both of them?

(2) Does the reason for my 2 years of residence matter in order to count for the 2 years of residence (for example, does it matter if I reside there for work, study, etc?)

(3) I have read the citizenship application may take two years after I apply, and I can't apply until I've been living there for 2 years. Do I have to reside in Spain during this process, or can I leave the country after the two years?

If you can provide any links to the legal documents that confirm the answers to these questions, that would also be very helpful. Thank you so much in advance for the clarification!

Sincerely,
Christine