1, the so-called calligraphy is a running script, and cursive script is not suitable for communication with people, and it is an art form. You already have a regular script foundation, so it shouldn't be difficult. Practice hard pen running script again.
2. The difference between a writing brush and a hard pen lies in the brushwork, that is, starting, transporting and collecting the pen. But also a character frame structure. Good for you, too.
Wish you success!