JD what era are you looking at for those characters you listed?
Past decade or 80s through now?
For good solo or
Silver Surfer-centric stories you need to hit the 90's. His solo title has The Herald Ordeal which is a great read. As are the Infinity War events. Danny Ketch
Ghost Rider in the 90's, up through about issue 50 is good material.
Moon Knight is fairly good up through about issue 40/45 if memory serves in the early 90's.
For
Nova you're going to have to read
New Warriors. He hadn't yet regained a solo book in the 90's after having one in the 70's. I don't think you go wrong with the first 25 issues of that for sure.
Guardians of the Galaxy 90's really doesn't resemble the one Marvel has tossed at us currently. Some overtures but it's different. I really loved the first 25+ issues of that as well.
Runaways I don't know.
Thor in the 90's was a mess. I dropped it, the art got bad and the stories very bizarre...even for Thor.
This decade though both the long running
Ghost Rider (36 issues) and
Moon Knight (30 issues) were both good imo. I even liked the shorter lived Vengeance of MK (10issues + Shadowland 3ish-mini) but admit some thought it uneven.
For
Thor start with the JMS material when he brought Thor back after
Dissasembled in 2007. The title then goes back to the old numbering for an issue #600 gala.
Surfer hasn't really had much. He had a recent mini but it was nothing to say 'must read'.
I've not read any of
Nova but understand his part in the Annihilation War was crucial and a good character piece. Maybe someone else can chime in on that.