The best way to get legitimate access to Umineko manga is to purchase or borrow from a library. Trying to find raw scans elsewhere is not recommended as it's often against the law and doesn't support the creators.
It's hard to say precisely. Different sources could have different counts. I suggest looking at dedicated manga tracking sites or following the official announcements from the publisher.
Well, determining which manga chapter the JJK anime is on is a bit complex. Different arcs and storylines might have different alignments. It's best to consult dedicated manga and anime forums for detailed discussions and clarifications.