Aveirah, the third was against the other nations, that they should not subjugate the Jews excessively.
IIRC (it’s been a long time since I learned Kesuvos), there was another opinion that there were 6 Oaths, the additional 3 being not to hasten the geulah, not to push it away, and not to share the secrets with the other nations.
Regarding the quotes from R Meir Simcha and from R’ Kluger, they are brought down in the sefer HaTekufah HaGedolah.
Aveirah, I hate to say it, but you are committing the same sin as the miraglim.