Genealogy / What does my Polish name mean? [401]

Hi everyone! So I have some questions about my family's surnames that have popped up in my genealogy investigations.

First my surname is Rólka, which has a variety of spellings in my family (Rolka, Rulka) but one that popped up that I'm confused about is Rolko. At least one baptismal record has Rolko and a cousin of mine in Poland who does genealogy has our surname as Rolko for a lot of my direct ancestors tho Rolka/Rólka will appear in parentheses but for a number of cousins it's only Rolko. The Slovak equivalent of my surname ends in -ko but our Rolka/Rolkos are from northern Masovia/southern Mazuria (Mława, Lidzbark Welski, Płock areas). Is there any reason that could possibly account for this variation?

Second question, one of my great grandmother's appears in marriage records for her children as Anna z Kaliszów. While I know z. d. can mark maiden names, does having z + maiden name in the plural genitive play the same role in these sorts of documents (late 19th century)?

Third question, not about surnames but how common was the first name Szymon among non Jewish Poles in the 19th century? I have a great grandfather with the name Szymon Stawski and I'm curious if he's likely Jewish or not.

Thank for any insight!