Torrent can not only run at breakneck speeds and jump remarkably high, including a double jump, but it also has the unique ability to come back to life if it perishes so overall I think he would be pretty useful in a lot of situations.

The reason Torrent is currently at this speed is because he is part of Miquellas' quirk, and his quirk is still in its infancy stage. As he trains, Torrent will get faster.

If you're asking if the character was originally someone else, then no - she was created by the same being as Marika, but she has her own distinct personality and thoughts within the story. She just looks up to Miquella.

No but he will age slower than most

It was honestly a mistake on my part I thought I added some dialogue in about this but I forgot, and while he will keep aging through the story his quirk does slow his aging

At the beginning, he is nowhere near the power we see Miquella possess at the end of the DLC, but he will eventually reach that level. As for your other question, you'll have to wait and see.

in the story he really will only use the rasengan if he has either ran out of clay and or there Is no other option and he will think of more ways to use his clay abilities so you guys don't have to worry about him just spamming the rasengan.

this is what I think the mask would look like (and while I said anbu mask now that I look at it more it reminds me of a hollow mask)

I decided not to change much on the first chapter the only thing that really changed that matters was he already has the jutsu scrolls

this is what I imagine his mask would look like