For this word:
1) /rekə/ is the first syllable. Does it contain two vowels?
■ e is a vowel
■ ə is a vowel
I thought syllables can only contain one vowel?
2) the [ ‘]symbol before /rekə/ means that /rekə/ is stressed. So why is the “o” in “reco” reduced to a schwa? Do stressed vowels get reduced? I thought only unstressed vowels got reduced.
3) Do words only have one stressed syllable or can they have two stressed syllables?
Syllables can only contain one vowel or diphthong (although different dialects of English may disagree as to whether something is two vowels or a diphthong—idea has three syllables in American English and two syllables in British English).
The word /ˌrekəˈmend/ has three syllables, /rek/, /ə/, and /mend/. In phonetic notation, you are not required to put a divider before unstressed syllables, although you can use a dot; if you do, the notation is /ˌrek.əˈmend/.
Can words have more than one stressed syllable? No and yes.
The general theory is that all words have exactly one syllable with primary stress, but some words also have secondary stress on another syllable. For example, in /ˌrek.əˈmend/, /mend/ has primary stress and /rek/ has secondary stress. For very long words, (like extraliterary) it’s possible to have two syllables with secondary stress: /ˌek.strəˈlɪt.əˌrer.i/ (American pronunciation; I don’t know what source you used for your phonetic notation, so my notation may not agree with your source’s.)