@P.J. The adventure makes for a good memory, but was a bit frustrating at the time. The layout of the buildings often have escalators or elevators which only go one way, so you have to get off at one floor and find the next on the other side of the floor. Makes for a lot of extra walking, but interesting all the same.
There was a thread started shortly after I got back from Japan to discuss the language, but it seemed to have died pretty quickly. I don't mind giving responses to questions to help out, but don't think there's really enough people studying the language to devote a constant thread to the topic.
With regards to the double vowels, just think of it as an extension of the first. The language really doesn't have the compound sounds associated with English, such as ai in paint, but does have these. When you see the u following an o, it gets pronounced as such. In the end, it sounds like you're saying o twice, but anyone familiar with the language will hear the sound difference. As a rule of thumb, except in the case of wa as in watashi wa and he used to imply where you're going or came from, Japanese kana will always use the same sound.
Once you get used to the sounds associated with them, and recognize the different meaning of the particles (you mention wa, ga, and ka, but there are quite a few more) it gets easier to recognize what is happening between the nouns and verbs in a sentence.
For example (in romaji):
I can say watashi wa, and it implies that I am the subject of the sentence which follows.
I can use watashi no, and it implies that I own something.
If using watashi ga, it implies that I am the subject of the statement, but my presence in the statement is new information not previously used in the conversation.
If I say watashi mo, it's the same as saying "me also"
The particles don't always hold the same meaning, but are actually associated with the noun or verb immediately preceding or following them. itsu is usually used to ask a question about time. Most normally can be thought of as translating to "when". However, I can say itsu ka and it would translate to "someday". itsumo is "always".
"mo" can be a bit of a tricky particle also. Even though itsu mo means always, you can't assume that the particle always holds that all inclusive meaning. If I say dare ka, it would still come through with a similar meaning as itsu ka and means "somebody". However, dare mo (rather than having the all inclusive meaning of itsu mo) actually means nobody.
As a beginner, it's a lot easier to get used to how the particles match up to various phrases. A lot of verbs have a single particle which will always be used with them. The first that comes to mind is sumu (sumimasu and sunde are the most commonly used conjugations). This verb will ALWAYS be preceded by the particle ni without exception. Those associations are important when you start trying to speak the language freely (not reading from a page) because you can create some rather messy/contradictory sentences if the wrong particle is used.
Best advice for particles is to get used to what they mean when compounded with each of the associated words. There are a lot of exceptions, but once you get a feel for what each means (and recognize the need for exceptions) it gets a lot easier.
A LOT of anime translations get screwed up when it comes to particles, and especially the older shows. Even now, watching To-Love-Ru currently, watching the romaji subs of the opening theme (I like the song, so listen to it at the start of every episode) I see A LOT of phrases which are actually 3-4 words ran together into one long word because the translator didn't realize that what they were seeing was a phrase. If a new learner were to see this, there's no way on earth they would be able to look up those printed words and get an actual definition. Recognizing the particles and conjugation (and how to switch to dictionary form) anybody would be able to translate the song and recognize where mistakes were made in the actual translation.