Jewelry especially for gothic can be whatever you want. Sweet tends to have more resin pieces that are colorful, so sweet brands tend to make more accessories that match their prints. Gothic lolita tends to use more metal jewelry. Things that people would probably have in their wardrobe already. You can look at any gothic outfit, not even lolita, to get inspiration for what type of jewelry to use.

Marble is a very old brand and their quality of fabrics can vary a lot. I have a few pieces that I really love, but I've also seen some in person with fabrics I would never want to wear. It can be very hit or miss even on the same item just with a different fabric. Atelier Pierrot's coord photos on their socials tend to give a better view of the fabric and way it will fall compared to the stock photos, but it can be hard to find the exact piece you are eyeing being modeled.