Features of Gaelic 1: Orthography and Brown or White Bread

I've figured out that there are only two episodes of SOL a week on BBC Alba, meaning that I never missed an episode last week. Last night I learnt how to say where I am from:

Càit a bheil sibh a' fuireach?         Where do you live?
Dùn Eideann                                Edinburgh
Dè an seòladh a th'agaibh?           What is your address?
Dè an aireamh fòn a th'agaibh?     What is your phone number?

One of the interesting and unusual features of Gaelic is its spelling. To the outsider, it seems as though there are far too many letters for the corresponding sound. And yet, the spelling makes more sense and is more consistent than English orthography. Many of the letters are there due to what I think of as the like-for-like rule, or the brown bread/white bread rule.

It's all about sandwiches
When you make a sandwich, you usually use two slices of the same type of bread. If you have a slice of white bread at the bottom, you'll use another slice of white bread on top. The same goes for brown bread, and it would be strange to mix the two. The same applies to consonants and vowels in Gaelic.

There are two groups of vowels in Gaelic and each group has a different effect on the pronunciation of the adjacent consonant. The two groups are called broad vowels and slender vowels.
Broad vowels are a, o and u.
Slender vowels are e and i.

Now, unlike other languages such as English or Italian, vowels in Gaelic have an influence over the preceding consonant as well as any following consonant. For example, the letter t changes from the t in 'toast' to a sound more akin to the t in 'tune' (what is called palatisation, or the insertion of a y after the sound). This means that the word càit (where) above is pronounced similar to the English word 'catch' by virtue of the i preceding the t. Make sense? Basically vowels are more 'influential' over adjacent consonants than in English or Italian. Easy, I'd say.

Yet there is a problem. What would happen then if you had a consonant with two different types of vowels on either side? Would you pronounce it broad or slender?
Gaelic's solution to this problem is to make sure that each consonant is only surrounded by the same type of vowel. It only uses the same type of bread on either side of the filling. White with white, brown with brown; slender with slender, broad with broad.

This is why fuireach (stay/live) above has an i before the letter r and an e after the r, even though neither are really pronounced distinctly in the word. Their purpose is to indicate how the r is to be pronounced (in this case, it is approximate to the 'th' sound in 'father', but lighter and less distinct - blooming difficult!)

Anyway, I'm sure my explanation is horribly complex and there are easier ways of doing it, but I like the white/brown bread idea. It also explains why there are so many vowels all over the place which aren't even pronounced.