Japanese grammar and vocabulary questions?

Question:

Hi, it's me again. I have several questions regarding Japanese grammar. Please help me! Yoroshiku onegaishimasu!

(1) I've been looking for the word that sounds like "seippai". May I know how it is spelled and what does it mean?

(2) What is the difference in using "darou", "desu yo", and "deshiyou"?

(3) I've been noticing some people end their interrogative sentences in conversations with "kai" ex., "daijiyoubu kai?". When and how do you use "kai"?

(4) How do you translate this in Japanese?
"Grades are something but not everything". By "grades" I mean the marks we get in school. And I mean that it is important (it is "something") but it cannot fully define you as a person (it is not "everything")

Thank you so much!

Answer:

1) I think you're talking about "seiippai 精一杯"
http://ejje.weblio.jp/content/%E7%B2%BE%…

2) If it's colloquial,
"darou" --> male/casual: e.g. "sorewa machigai darou" (that should be a mistake)
"desu yo" --> unisex/ polite: "sorewa machigai desuyo"
"deshou"(not "deshiyou") --> unisex/ female/ polite/ mild: "sorewa machigai deshou"

3) "...kai" is a colloquial ending form of question mostly used by men(adults)

4) 成績には意味があるが、それが全てではない。（written）
seiseki niwa imiga aruga, sore ga subete dewa nai.
成績は大切だけど、それが全てじゃないよね。（colloqual example）
seiseki wa taisetsu dakedo, sorega subete ja nai yone.
*意味がある：meaningful
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