"A pig is not small."
Translation:Chan eil muc beag.
The course is still in Beta so I imagine that will come.
However, this may be of use to you.
General rule is that when you have two vowels, one broad and one slender, and no suspicion of a long vowel (accent, or a double letter following) then you pronounce the first letter in Gàidhlig and the second in Gaeilge. The y you mention just results from the slender b. The first vowel is the historically correct one (Old Irish bec) and the second one was added at some stage for some reason.
Yes dona just means 'bad'. There are actually lots of words in Gaelic with 'bad' meanings beginning with do and they almost always have an opposite beginning with so. In this case, sona means 'content, happy'. Just see the do or so section of the dictionary for lots of examples.