I've been told that Toeto is a fairly simple song. I second the suggestion of 40mP too (:
I wouldn't consider myself as someone who knows Japanese, as I can only read some hiragana and katakana and I can only understand some words and phrases due to having watched a lot of anime, but I sing in Japanese nevertheless. I think many youtaite don't know Japanese and it's totally fine on Youtube. I'm not so sure about on Nico Nico Douga, though; I haven't looked at comments much there so I don't know if people there would judge someone harshly for not being fluent in Japanese.
Another suggestion for your 1st question if you're using PC: I download the video online, then I open up Windows Movie Maker and import the video. I mute the video's volume, import the audio file for my cover, and then save this new video so I can upload it to YouTube.
Hmm, well, I feel like learning to mix was something I did gradually over the years, though I still don't feel like I know very much about mixing. But I think it would be relatively quick to learn to use a few basic effects c: I use Audacity, a free program, to record and mix. Some effects that you may want to use are Amplify, Compression/Compressor, Mastering, EQ, and Reverb (these effects are generally found in many different programs but they may have slightly different names).
I guess if you can find someone who's willing to draw for you for free, that's great c: Just make sure you show your gratitude to them, and maybe help share their artwork, and if they're doing commissions be sure to spread the word that they're taking commissions. Would be even better if you are able to pay the artists.
I agree, definitely try to get a mic as soon as possible. I recorded my first cover with my headset but the audio quality was not good or consistent, so after that I bought myself a mic (I use Audio-Technica AT2020). For software, I second the suggestion of Audacity. Reaper is also free (it will have a pop-up window when you start the program that asks you to buy it but you can say you're still testing it and keep using it for free indefinitely). Garageband could be an option if you've got a Mac.
My skype is kaisoumizu. Feel free to add, but let me know that you saw me on utaite wikia so I'll know to accept you xD
Some other places to find youtaite: YTChorus forums http://ytchorus.forumotion.com/ Facebook groups such as Youtaite Mix, Youtaite Academy, etc.