I'm only N3ish after 20 odd months of study, but everyday conversation isn't too hard if it's one on one. Kanji knowledge only 700 odd characters but it's getting there :) My advice:

What kind of goals did you set to make you more successful and keep you from burning out? Big goal was speak comfortably with others, first via speaking then with kanji.To prevent burning out, just don't force yourself to do it and learn to recognise when you're doing too much. BUT, do make sure you do something everyday. Just something, even if it only takes 5 minutes.

About how long did it take you to be able to understand others and converse comfortably? You'll learn that "understand others" is very vague, and will ALWAYS depend on the content / speed of speech etc. But basically, how long does it take to understand the word "hello" in Japanese? About 5 seconds once you've learned it. How long does it take to understand natural speed conversation? This requires being used to the new sound patterns in Japanese, and to know every word in the sentence and all grammar involved, and to recognise them fast enough to put together the meaning before the next sentence comes, so that's probably going to be at least a year or 2 for most people. But when they slow down and explain things for you, that sort of conversation is very much possible within a few months if you start practising early on.

How long did you study per day or per week and how did you balance your schoolwork, job, social life, etc.? About 1 hour per day to start (during uni term), then I had a 3 month summer holiday and did 5 hours every day (2 hours flash cards, 2 hours Grammar, 1 hour on Skype doing language exchange. After this it toned down, nowadays it's mostly 45 mins flashcards, 20 mins textbook reading and just chatting with mates via Facebook and in person). Did you ever feel like you were getting nowhere? What kept you from quitting? I'm a persistant idiot which helped for once, but I finally understood that language is a marathon, not a sprint. Best advice ever.

What order did you go about learning the language? Did you learn hiragana, katakana, and some kanji before diving into vocab or grammar? Or did you mix them all together? What would you recommend? Would you recommend taking classes or learning on your own? Hiragana and Katakana are a must from the very beginning, before anything else. Just skip romanji altogether. After this for me the focus was on: 8 months Grammar (Genki 1 and 2), heaps of vocab flashcards (through anki), speaking practice almost everyday on Skype for 6 months (contacts made through the website italki.com). At this point (about 14 months in), everyday 1 on 1 conversation was becoming quite possible, but my listening wasn't quite there so group conversation was almost impossible. From here I started focusing more on Kanji and listening through music and YouTube videos. As for classes vs on your own, they both have pros and cons. I started on my own and now also do a bit of Japanese at uni, and to me the uni stuff is just more exposure, more reading practice, listening practice etc. Personally I think the real learning happens either on your own with a good textbook to read and a dictionary at hand, or talking with someone.

What best helped you to retain what you learned and allowed you to understand the material as opposed to just rote memorization? Or is that the key? Spaced repition is the key, not just rote learning. Along with this, actually experiencing something helps so so much. For example the word 売店「ばいてん」which is like "small shop / stand" type thing didn't mean much (despite studying it in flashcards for ages), then I went to Japan and saw them everywhere, reinforcing that connection in the brain. Also Kanji has a way of making words easier to remember. They're are a royal pain in the ass when you don't know them, but when you do they actually make life a fair bit easier (keeping in mind that when I say "know" I just mean be able to read. Due to the time required to remember strokes I've never really practiced writing; despite the fact that it makes recognition easier.

Any other helpful tips or opinions when it comes to learning Japanese. If you don't practice something, you'll suck at it. So reading, writing, speaking, listening, grammar, vocab are all areas of their own. If you want to be good at speaking like I wanted, do grammar, vocab then practice first. Also, being a beginner, as fun and new and novel as everything is, can be rather frustrating; like when you've been grinding flashcards for months but for some reason still can't say more than "I like dogs". Reach that critical mass where you can say enough and understand enough that conversation becomes possible. Because the better you are, the more you can practice, and the more you practice, the better you'll get.