海 is ‘umi’, or sea/ocean. You are correct that the second half of the kanji (母) is the same as the standalone character for mother, but it’s base radical is ⽏, which also just means mother. The first radical, ⺡, means water/ liquid, so you can sort of infer that “water mother” = ocean. Not all kanji work out this nicely with their radical structure, though.
Last part is spot on, ikou (行こう) is the shortened (conjugation?) of iku or ‘to go’ that expresses a suggestion to do, i.e. “let’s (go)”.
Yes, 君 is ‘kun’ when used as an honorific.
海 is ‘umi’, or sea/ocean. You are correct that the second half of the kanji (母) is the same as the standalone character for mother, but it’s base radical is ⽏, which also just means mother. The first radical, ⺡, means water/ liquid, so you can sort of infer that “water mother” = ocean. Not all kanji work out this nicely with their radical structure, though.
Last part is spot on, ikou (行こう) is the shortened (conjugation?) of iku or ‘to go’ that expresses a suggestion to do, i.e. “let’s (go)”.