The length of syllables is independent from the number of syllables.
Yes, pronunciations vary by accent, even by individual (cf.
this).
By real vowel I mean a vowel that is in the RP English phonemic inventory (what else would make sense since we can't hear each-other on the intarwebs?). Two vowels together count as one if they're a dipthong, tripthong, or denote vowel length. I can see why you might think the [ea] in "nuclear" is the dipthong /ea/ and thus a single vowel, but it isn't. The [ea] in "nuclear" isn't the same as the [ea] in
near, and
clear. In words like near and clear the [ea]
is the dipthong /ea/. However, in the case of "nuclear" the [ea] is two separate phonemes.
I've never heard the "clear" part of "nuclear" pronounced the same as the word "clear". So, if you have the means, post some samples of your pronunciation of some words with [ea] in similar environments. (Make sure to pronounce them as you would in conversation. Also, try to them in a sentence. Don't try to pronounce things slower/faster, extra clearly, or with special diction. That distorts what is produced and heard.)
Squirrel is really tricky. I'm not touching it with a ten-foot pole.
I am not a phonologist, I just play one on TV.