descendant of Finnish citizen Residence Permit Question

I'm interested in applying for this residence permit, but am finding very limited info about it online to determine whether I qualify. Hoping someone here has some better info to share!

I think my eligibility basically boils down to whether my great-grandfather (born in Finland) and grandfather were Finnish citizens. My father was also adopted (by the aforementioned grandfather), which is another potential hurdle to clear.

My concerns:

• GGF was born in 1881 in present day Finland and immigrated to the US in 1913. He filed a petition for naturalization in the US in 1918. Finnish independence was declared in 1917 – does this mean he was ever a Finnish citizen?

• GF was born in 1928 in the US – does his birth occurring after GGF's probable naturalization break the chain of citizenship passing down to him? Though my GF (and F, as a minor) lived for a number of years in Finland, I'm unaware of either of them ever having taken action to retain citizenship, nor is my F. I think him (probably) having lost Finnish citizenship at 22 is okay, since the residence permit only stipulates "at least one of your parents or grandparents is or was a Finnish citizen by birth."

Does GF potentially having never obtained a Finnish passport/registered with Finnish authorities as a Finnish citizen create any hurdles if clear lineage to GGF can be established? Specifically, I'm a bit worried about establishing the below requirement:

Certificates from Finnish archives verifying Finnish citizenship (e.g. official certificates from parishes, certificates from the Finnish National Archives)

• F was born in 1964 in the US, and was adopted by GF. Though he doesn't know identity of birth parents (but is possible to find out due to a recently-passed law in his birth state), he knows they were also Finnish and thus may be an alternate route to pursue, if Finnish law offers this as an option.

• I was born in 2000 in the US

I have birth certificates for F and GF already, and can get them legalized. Am I missing anything else that may be a hurdle with this application?

Thanks in advance!