Is STC worth reading? I read the first 10 issues or so (only the Sonic parts, since I wanted to focus on them) and I couldn't continue. I'd like to know if I left before it got good.
Definitely. The cartoony, questionable quality of the earliest strips rapidly gives rise to something much, much better in later ones. While StC takes more cues from AoStH (likely to contrast it to Archie taking cues from SatAM), it's definitely a very interesting experience overall since it depicts Sonic in ways that no other continuity does; the main writer took a lot of liberties with each character he was given, especially Sonic himself.
But overall? While it had very silly one-shot stories, just like Archie, it gradually developed a more coherent plot after about twenty or issues and became a really good read fitting for serious viewers and not just casual readers.
Above all, if you want a testament to the power of StC, just look at Sonic the Comic Online - it's been going for ten years with dozens of issues released, all without a single penny paid to those who work on it. Now that's devotion!
Also, as a bonus to you based on what you said: in later issues they phase out the non-Sonic stories entirely in favor of giving exposition to other Sonic characters.
It's a given that Sonic's not married. Flynn wouldn't bother specifying that Sonic was single unless he isn't involved in any form of romantic relationship.
Indeed, Sonic's been banned from marriage for a really long time. It's why the Mobius: X Years Later universe is described as a "possible future" - SEGA refused to approve a for-sure future where Sonic was married and had kids.