Pronunciation of double vowels?
For words like scii or praavo, do you pronounce them as sci-i and pra-avo (using a glottal stop) or do you just lengthen the vowel sound? or doesn't it matter?
Esperanto has the one-letter-one-sound scheme. And every letter needs to be pronounced.
So, scii is spoken as sci-i and so is equivalently pra-avo.
How you'll manage to make the doubble letters hearable depends on the speaker. But you'll often hear a "little" glottal stop or a change in the tone.
(I'm not sure if the glottal stop is explicitely mentioned with Esperanto at all, though)
As ThorusCrusius mentioned there is often a "glottal stop" - similar to the way we pronounce "uh'oh". It's not officially part of Esperanto.
If you watch Pasporto al la Tuta Mondo, you might notice that the teacher says "Rigardu, aŭskutu, kaj ĝuu" before each episode. In the earliest episodes, she seems to make the "uu" one long sound. It seems that there were comments after the first few episodes came out because in later episodes she clearly (and correctly) pronounces it as two sounds.
Keep in mind that in scii, praavo, and ĝuu - one of the vowels is accented and the other is not.