This site and other sources say that there can never be two consecutive vowels in Turkish. Does this only apply to cases where a suffix is added to a word or is it true of the whole of the language including single words???

Cheers, Bod xxx

As far as I know, it concernes all the words, not only suffixes. But there are some exceptions like "saat" and also other words that are Arabic in original.

Good question.
It applies to suffixes.
Example:

Dative Case Suffix: -e -a (meaning to, towards)

If the last vowel is a deep vowel (a,ı,o,u) we use -a
okul+a :to the school

If the last vowel is a sharp vowel (e,i,ö,ü) we use -e
deniz+e :to the sea

But if the last vowel is a deep vowel (a,ı,o,u) and the word ends with the vowel we put the bufer y inbetween:

su+ya: to the water
hava+ya: to the sky
Ankara'ya: to Ankara

But if the last vowel is a sharp vowel (e,i,ö,ü) and the word ends with the vowel we put the bufer y inbetween:
kedi+ye: to the cat
Türkiye'ye : to Turkia

http://www.turkishlanguage.co.uk/nouns.htm

There arent many. Just a few. In fact right now I cant think of others. Saat is the most common.

By the way, all the suffixes follow the rules.

vaat: promise
vaaz: homily. sermon
taarruz: attack
müsait: convenient. suitable