It's also possible to set your English keyboard to "English International", which will allow you to type the accents needed for Gaelic, German, French, Spanish, and Portuguese (and maybe more?). It will change how your keyboard functions when you use the keys that would then have dual functions. It took me a couple weeks to get used to, but it's second nature now, and so convenient for typing those languages. If you want to know more, reply here.
Isn't the -ag suffix specifically a feminine diminutive? Which was my thought about the derivation, as it supposedly means "princess". It struck me when I was reading The Lord of the Rings. "Ar" is "great" (or big) in high Elvish, like mòr in Gaelic, and "wen" is a feminine diminutive. So Arwen. The princess. I think.
So the princess's name was Arwen but that does not make it likely that this name means 'princess'. I think it just means that Arwen and Mòrag are semantically equivalent.
There is a lot of dialectal variation. Words that end in a g can be anything from /k/ to /g/ in practice, though most teachers say it should be /k/. When not at the end of a word it is generally /k/. But either way it is generally accepted that some sort of difference is maintained between c and g in each dialect. The usual story is that they used to be as you would expect. Then g changed /g/ → /k/. This then resulted in c changing, to keep it distinct, usually /k/ → /ʰk/ (the so-called pre-aspirated c). Compare
aige /ˈekə/ — aice /ˈeʰkə/
Sometimes, especially in this word it can be very strong, even /ˈeçkə/. Before anyone complains, yes there is tons of variation. You can hear various vowels at the beginning and it 'should' be /kʲ/ rather than /k/.
This then gets complicated. They are pronounced 'normally' as first letter of a word. After a consonant (e.g. in school) it is still a /k/ sound but because of the perception that the pronunciation of c had changed except when first letter, this word had to be respelt, from Irish scoil to Gaelic sgoil just to show the pronunciation had not changed.
Some words changed from c to g because of the pronunciation in some (now largely forgotten) dialects. This is why some words such as beag (Old Irish bec, Welsh bach) are pronounced with a /k/.
Then we have agus. This originally had a c in it (Old Irish ocus) (and compare Welsh _a(c)) but the pronunciation changed, most unusually, in all dialects. This means that in many dialects it is the only word that has a /g/ after a vowel, and consequently there is no way to represent the sound in the standard orthography. So you just have to treat it as irregular.
Does that clarify matters?