*edit* Sorry...I posted kinda late .___. Technomancer, you posted while I was busy writing this ^^;;; Hehe. *end edit*
I've never heard "ko me no sai" before...o_o You can also say "gomen ne" and mean "sorry". And "sumimasen" can also mean "excuse me". I'm not exactly sure what "nasai" literally translates to but they use it at the end of a lot of things...I think it's a politeness thing. There are some differences between polite speech and casual speech...like, "chotto matte kudasai"/"hold on a sec"-- the "kudasai" means "please", if I remember right.
Also, with the suffixes, never ever use them in reference to yourself. It's considered impolite O_O
Here are some pronouns
Watashi, atashi, watakushi, boku-- I, me. Hehe. "Atashi" and "watakushi" are more likely to be used by a female, "boku" by a male.
Anata, kimi-- you. "Kimi" is usually used by a male in reference to a female. Or at least that's what I understood...
Hmm...I can't think of anything else. So uh, I'll go do something else now >_> .....^^;;;