A question for grammatically aware Norwegians

Or anyone who knows more Norwegian grammar than I do, really.

Recently—after years of not quite getting round to it—I’ve started learning Norwegian. Or attempting to. Searches for evening classes and the like proved fruitless, as did searches for affordable Norwegian-learning books, so I’ve had to come up with my own process for learning the language. The basic process is:

• Take a fragment of Norwegian, such as a tweet from one of the Norwegians I follow on Twitter. (Twitter is ideal for this! I never have to try to understand anything more than 140 characters long.)
• If I don’t understand it and don’t want to look up all the words straight away, use the Opera Inline Translator extension to get a somewhat garbled, but still helpful, idea of what it means.
• Look up any new words in the rather thin Norwegian dictionary I managed to get hold of. Also,  if possible, look up the component parts of the words.
• If I don’t understand how the grammar fits together, either look up the relevant section of Louis Janus, Norwegian Verbs and Essentials of Grammar or make a note that I need to. (It’s not sensibly possible to learn all grammar at once, even a tweet at a time. But it is possible to add, say, “adjectives with definite nouns” to a list of things to put off learning learn later.)
• When in doubt, plague ask a Norwegian. with questions

Today I thought it was time I got to grips properly with the past tense and past participles. (Just for regular verbs; irregular ones are their own particular nighmare.)

Apparently Norwegian regular verbs are grouped into  four classes according to what ending they use to form the past tense: -et or -a for Class I, -te for Class II, -de for Class III, and -dde for Class IV. Past participles are the same but minus the final -e. The book makes some comments about what kind of verb typically belongs to each class.

“Is this Class I, Class II, Class III or Class IV?” isn’t really the sort of question one wants to be asking when looking at a word. The relevant question is “what ending goes on this, and why?” So I’ve tried to re-work the information in the grammar book into something which is easier to remember and use. I came up with these rules of thumb below. They’re just for regular verbs, and I know that irregular ones won’t follow them. But hopefully, if my rules are right, I’ll be able to tell what the irreguarities are, and that will make it easier to learn them.

Here’s my attempt:

• The basic past tense ending is -te after a consonant or -de after a vowel.
• But Norwegian doesn’t like triple consonants. So if adding -te would produce three consonants in a row, use -et instead (or -a if it suits your dialect).
• However, -ldte and -ndte are OK, since -ld and -nd act like single consonants. Also -ll-, -mm- and -nn- will be contracted to -l-, -m- and -n-, so the -te ending is still OK for verbs whose stems end with those.
• A -g or -v at the end of the verb stem softens the ‑t in the ending to ‑d, so we get -gde and -vde (not -gte and -vte).
• If the verb stem ends in a single, stressed vowel, then the -d in the ending is emphasised too, by doubling it so the ending is -dde.
• For a past particple, use the same endings but without any final -e.

Or more briefly: for regular verbs

1.  Use -te after a consonant and -de after a vowel.
2. If a triple consonant other than -ldt or -ndt would result, use ‑et (‑a) instead.
3. -g and -v soften –te to -de.
4. A single stressed vowel strengthens -de to –dde.

And my question is: do these rules seem right?