That's quite a judgmental generalization, Zawerg. Duden indicates that [ˈkafeː] is the standard pronunciation, while [kaˈfeː] is an Austria variant. See also: http://www.atlas-alltagssprache.de/runde-4/f23a-c/ http://prowiki.ids-mannheim.de/bin/view/AADG/KaffeeAkzent
I grew up around native German speakers (I'm now relearning the language) and "ee" is typically pronounced "ay" as in the name Beethoven. These recordings where "ee" is pronounced as would be in English make me crazy. For the word Kaffee, "kaFAY" is what I have always heard spoken. "Tee" would be "tay."
Have a look at the tips and notes for the very first unit again -- I think you'll find that your question is answered by the second section of https://www.duolingo.com/skill/de/Basics-1/tips-and-notes .
Please always read the tips and notes before starting a new unit.
To do so, go to https://www.duolingo.com/ in a browser (the tips and notes aren't available in mobile apps for German), click on the lesson unit, then on the lightbulb icon:
Listen to it here: https://forvo.com/word/und/#de
Basically it's supposed to be like unt.
In fluent natural speech, it can sometimes sound like un -- a bit like how English and in fluent natural speech sometimes turns into 'n' as in this 'n' that. But that's not the "default" pronunciation.
Best to start with the "proper" pronunciation and let colloquial slurrings and contractions come naturally later after you've heard and spoken a lot of German.
Neither of these words are feminine, though, nor do they end in -ei. Nor do most feminine words end in -ei in German. There are a number of endings or even none at all.
That's a lot different from Spanish.
It really does seem like less effort to just remember each individual word's gender than to memorise the complicated list of endings for each gender (and then still have to remember the ones that don't have any specific ending).
Here's a tip for finding the article of a noun. Go to Google Translate enter "the tea" (not just "tea") and translate it to German. It will give you the article.
Remembering the correct article has always been one of my biggest stumbling blocks with German. This time I am doing flashcards to practice the nouns and it is helping.