I would think that "Mi sidis, legante libron" translates as "I sat, while reading a book." Is this incorrect?

Anyway, I personally like the way the -e ending sounds.

Borgo:I would think that "Mi sidis, legante libron" translates as "I sat, while reading a book." Is this incorrect?.

I would say that you are right; the ante form is used to say "while doing something". Also, the sentence may be clearer if you place the ante form first. But would anyone emphasize sitting in this way in relation to their own reading? Note that the above is not saying "I read a book while sitting." That would be "Sidante, mi legis libron". If you wanted to emphasize that you passed time by both sitting and reading a book you might say Mi sidis kaj legis libron.