I buy sheets of paper and cut them to size. I use Strathmore drawing paper a lot. It's not excellent at holding most inks, but it's Ok and it's fairly stiff, which is good for cards. Clairefontaine Triomphe paper gives great crisp edges on the ink, so sometimes I'll draw on that and attach it to stiffer paper (https://www.jetpens.com/Clairefontaine-Triomphe-Notepad-A4-Blank-50-Sheets/pd/10365).

There are tons of kinds of papers and nibs and quite a few inks. Mostly I'd say there's nothing bad, just different things have different uses. Art stores have racks of fancy paper to use for trim or other decorations. You'll want some standard nibs. Leonardt and Speedball sells sets. Some really fun nibs are the Brause 361 and Zebra G. For writing the Windsor and Newton calligraphy ink is really nice. For drawing I try out different brands or whatever color or texture seems nice for what I'm doing.

Just to get started, I'd get a set of Leonardt nibs (they come in a carrying tin) and a straight handle, black Windsor and Newton calligraphy ink, and any drawing paper stiff enough for a card. Then think of a card design and buy the colored inks you need of whatever brand.

The only thing in this hobby that has ever seemed crappy are the plastic nib holders with patterns printed on them. They dry out and split. I can't find a picture online, but every art store with nibs always has these holders too. The Speedball plastic ones are fine.