For the speed it's up to you to decide what looks good and what is best for your gameplay. I can't imagine what those different numbers look like in my head LOL sorry; I normally do it by frames and not by seconds.
As for the loops, some animations are designed to loop, some ping-pong, and some are meant as a single sequence. I believe that it's explained in the PDF Guide (if it's not, then I overlooked it and lmk so I can add it to an update!).
Thanks!