One answer I read on your site is that Hatarat Nedarim on Rosh Hashanah is for personal vows and Kol Nidre is for community ones. What is an example of a community vow? Aren’t all vows personal? I am having trouble applying the distinction. Finally, what is the source for the custom of hatarat nedarim on RH?

I haven't seen an opinion that Kol Nidrei is for community vows and it is clear from all sources it if for the individual as well. A community vow may be a vow the community takes as a whole for instance to build a new shule or fix the Mikveh etc. The Talmud [Nedarim 23b] states that one who wishes his vows to not count, should proclaim at the beginning of the year that his vows should not count which will help in case he forgets this proclamation. This is the source to parts of Kol Nidrei. The reason Hatarat Nedarim is said on Yom Kipur which is attached to Rosh Hashana is since most people come to Shule on Yom Kipur. [Shibolei Haleket] The Hatarat Nedarim on Erev Rosh Hashana appears in the Shlah with the reason of "Zrizin Makdimin" – the earlier the better.