Bernkastel does appear in the VN, though apparently fairly briefly. Sorry, I've only gone partway through Higurashi. I've read Umineko, obtaining a lot of my info needed to better understand Bernkastel's past through the web. She does have an expanded presence in the manga and an appearance in the Higurashi Rei novel Saikoroshi-hen. I personally just read what I wanted to know online and went straight to Umineko. As for Umineko, she has a large role in the second half of Umineko and appears a number of times of the first half. Go for the Umineko VN and avoid the anime.
As for sushi, it's alright. I've only had limited exposure to sushi though, nothing from anywhere good, just supermarket sushi.