I don't know - I think you can learn by pattern, and learning them all in isolation before you start sentences is a lot to take on. Tafarn / y dafarn - easy peasy! I've been learning Polish and every time I look at the rules I want to cry. For me, it's better to get on with learning some sentences, and that's the approach I would recommend
Well, tafarn in Welsh is feminine :)
An English word can have multiple words in Welsh, either as general synonyms (like "little/small" in English) or depending on the area/dialect, and they may not all have the same gender (for example, "key" can be allwedd, feminine, or agoriad, masculine, among other possibilities).
This course follows the patterns used in teaching spoken Welsh to adults. Many of the patterns are contracted from those used in the old course books for written Welsh. All the spoken dialects are different from the patterns used in course books for written Welsh.
These differences are explained in many of the notes of this course. The notes are available in the web and android versions of the course. If you're using iOS then the notes are accessible using a browser app.