(a) Why is the issue about carrying being discussed in the Mishna and Gemara
when all of the things mentioned are muktza to begin with? (b) Why the
amount of ink when one cannot write?
(a) Your question touches on an important principle. The prohibition of Muktzeh is a Rabbinical prohibition, and one who transgresses it has no obligation to bring a Korban Chatas. Carrying from one domain to another, on the other hand, is a Torah prohibition, for which one can be obligated to bring a Korban Chatas. The Mishnayos here are discussing the transgression of the Torah prohibition of Hotza'ah, and it is not concerned with the Rabbinical prohibition of Muktzeh that may also be involved.
(b) To be considered a bona-fide transgression of Shabbos, one must carry out an object (and quantity thereof) which has significance. The significance of an object is measured by its normal use during the week. Since this amount of ink is normally used during the week, it is considered a significant amount to be Chayav for carrying it out on Shabbos.
I am a novice at this and at 77 am beginning learning the daf. I use the ArtScroll Gemara.
Unfortunately I cannot attend a class (I'm still working B"H) with young
bechorim to support k"h.
Kol ha'Kavod! Your questions on the Daf were mailed out to all of our of readers, and in this personal note we just wanted to ask you if we could be of assistance in perhaps arranging a Chavrusa for you to learn the Daf with, in case you don't have one already. If you are interested, please let us know what city you live in and your phone number.
All the best!