Is there a natural order to things like this in Gaelic?
In English there are sometimes food pairings that - I think - we’d naturally talk about in a certain order (assuming a sandwich or plate of, rather than a random shopping list):
Bread and ham, bread and jam (bread first)
Herring and potatoes (fish/meat first)
Indeed, but you should be aware that agus is the standard - and the only version I had ever heard before starting Duolingo, including doing a course at university and listening to the BBC. ayus is valid but unusual.
It is an odd word, as even the g is a bit weird. It is an unvoiced c in Old Irish ocus and appears to be related to the words for 'and' that have a /k/ sound or similar in many European languages, and a /g/ only very rarely
Welsh: ac (+ an aspirate mutation that shows it ended in an s)
Old Norse: ok
Latin: atque, -que
Dictionaries do not usually relate all these words but I feel they must be related.
Because some words with g in became pronounced as /k/ they started using g to write /k/ (as in sgòil = school = Irish scoil) except at the beginning of a word. That means there is no longer a correct way to write the /g/ in agus and so it is an irregular spelling for a word pronunciation that should not exist.
On the other hand, pronouncing a g as a /j/ (y sound) is not found anywhere else in Gaelic but it was quite normal in Old English which is why we have yard beside garden and day next to German Tag. D