Thank you for telling me what 'Boxer' type, 'Freight Train' type and 'Don't think twice' type picking is in your eyes. Going to check out what you mean as soon as I can get some time. I did all those songs ago, but I did it 'my way' for the simple reason that I am a very bad listener and never can figure out how something is played. So I always have to find or not find my own way to do a song. Sometimes it just doesn't work but sometimes it also works some way that makes me being disappointed by the original when I hear it again. And some people also told me the same when they had heard a song by me first - these are things that really encourage me.
From that point of view, let me tell you, that aside of what you already pointed out there are still many more ways of doing it, some examples:
- Try to alternate between two different pickings. Some songs love that, especially those which need a stress on the first beat of every second ... err ... measure (is that correct?)
- Try using all three fingers for one beat, and then 'break' that chord by not playing these three tones exactly at once (don't know how to express it better, sorry). There are many ways to do this and each one sounds different. Then combine that with hammering an pulling off ...
- Look at what the banjo player are doing (i.e. not doing) with their thumb. I recently learned that the secret of the famous three finger style is NOT using the thumb on the first beat. Didn't find some way of doing this myself on the guitar yet.
What you'll get in the end is your personal guitar style. You'll be recognized by listening. Good or bad? Good.
But knowing all this - I never found a way to do a fast polka rhythm by fingerpicking. You know: Boom chick boom chick boom chick boom chick (no 'chicka')... Easy to do with 'classical' four fingers: th (i/m/r) th (i/m/r)... Some songs need that, e.g. 'Down By The Liffeyside'. Any hints?
Regarding picks: Hard to learn and when you're done it will sound different. Both for the same reason: If you play with your fingers you can sense the string before picking it. You'll do that because it makes everything much easier. This will damp the string with some significant effect to the rhythm. If you use picks you can still sense the string THROUGH the pick (you'll have to learn that), but only AS you pick it, not before. There is no way to damp the string with a pick, it will buzz. You have to keep the pick away from the string and then perform some exact curve with its tip to get the tone you want. Difficult but possible. And simply different. To me it sounds great sometimes, although I have not yet learned again how to do all the things I did without picks before. But I learned some additional things.
Hope that helps a little although it's hardly an answer to your questions.
Simply keep going on. (And also listen to what Jed says; I just learned that he's an excellent guitar player ;-)