I find that leaving a brief "u" sound helps to let the sentence flow. I don't say su-ki, but at the same time I don't say "ski". I just doesn't sound right. I say something in between.
I don't pronounce the "u" if it falls at the end of the sentence.
About 1dan and 5dan verbs:
5dan verbs end in -au, -ou, -uu, -ku, -gu, -su, -tsu, -nu, -bu, -mu or -ru.
1dan verbs end in -iru or -eru. However not all verbs that end in -iru/eru are 1dan verbs. Eg. Hashiru (to run) is a 5dan verb.
5dan verbs conjugate after the consonant:
While 1dan verbs conjugate after the vowel:
Eg. Miru>mi(ru)>mi(masu) or taberu>tabe(ru)>tabe(masu).
That's the basics of it. The reason they're called 1dan and 5dan (lit. 1-row and 5-row) has something to do with the gojuuon table (the ordering of kana), but I can't remember exactly what. Derek-san! Please help!