You cannot use the bucket on a lineart layer (with vectors), but you can turn it into normal layer and then fill areas with the bucket. Make sure there are no openings though, the color will run through! So make sure your vector lineart is complete and clean before turning it into normal layer. Good luck!
Ink pen and normal pen are very similar, ink pen is a bit smoother though and the color appear differently (try with various colors you'll see how it has really the "ink" feeling). But it works fine for lineart