Don't we need the t- since oidhche begins with a vowel?
Nope, that rule would only applies if it were a masculine noun. "Oidhche" is a feminine noun, and so its definite article is an. :)
I've noticed some courses have pronunciation guides in the tips section, but Gaelic doesn't seem to have this, unless I missed it? I'm still confused as to how to distinguish between pronouncing vowels with accents versus vowels without accents
Why is there no 'ann' at the end here, such as in bha deagh madainn ann ?