1) What you see is named Mojibake (those weird symbols that replace kana). You need to set your computer in JP locale or use AppLocale (to be honest, been AGES since I had been on a windows XP, so I can't remember the exact steps)
2) APPEND is a term created by Crypton Future Media to name a variation of the main voice of their VOCALOIDS. This term was adopted by most of the UTAU fandom. As I said, is a variation of your recording voice compared to your "main" bank. Ritsu's main voice is a soft one, while her appends are Strong Voice Material, Kire, Shout, and Power.
You can also understand the concept by listening to Hatsune Miku Appends:
【初音ミクAppend】±【全部入りテスト Append ALL】
Appends are archived via recording and not via flags.
3) The reason is the same you give on your question: No otos. The reason of why she is "skipping" notes is because she is actually singing the silence before the sample. OTO.INI is the back-bone of your UTAULOID and tells the program what it's ordered to sing.
To understand otos, please check:
http://utaforum.net/index.php?topic=3235.msg23519#msg23519
4) If by this you mean "how to be popular", please abandon this idea. Will only lead you to frustration and desire to quit. I am not being mean by saying this, but honest and giving you the best advice.
A way to be "known" is to be active: Work, Work, Work. The reason of why some users are more known to others is because of their hard work on their banks (otos, samples, etc), their mixing, their tunning, etc. Also a big part of this is socialization with other users.
5) Flags are orders that change the voice format. You can find the function of each flag on this page/manual:
http://utau.wikia.com/wiki/UTAU_User_Manual_-_7
I do recommend you to check all the chapters if you are a new user. It may be a bit outdated, yet will help you to learn the basics.
6) ACPT: Fixes envelopes by creating some kind of auto-oto. Avoid it at all cost.
P2P3 and P1P4: are adjustements of your previous note with the overlap of the next one. I recommend adjustement of the envelope only with P2P3.
OPT: Optimizes the crossfade of wavforms inside the notes. I do recommend you that, after rendering your ust by first time, click this, delete the caché, and re-render. Will give the final waveform a better sound (pretty useful in VCV sounds).
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I will also see convenient that you check how to adjust your ust to your oto settings.
http://utaforum.net/index.php?topic=393.msg1908#msg1908