Welcome back to the wonderful world of grim, dark future.
Now then, to your questions:
-The Sons of Medusa have no special rules attached to them in the current edition, if indeed they ever had any. Unless you have some really strong ideas about them, I'd play them as a standard codex chapter.
- The rulebook in the starter set contains all the rules, but none of the pretty pictures or pages of fluff. Those two sets are a decent start for a marine army, though you can't make any truly focused killer lists with them alone.
- In essence, you need to pick which codex you're using for your marines. If you play your SoM as standard codex marines, you can use Marneus Calgar in all his glory. I'd consider changing the name though, as Calgar is an Ultramarine. Your Bjorn dreadnought could always be used as a normal one, though you may have to file off the most obvious Space Wolf iconography. If you want Bjorns rules, you'd have to play your marines as a a variant of the Wolves, and then you can't use Calgars rules of course.
- I'm afraid I really can't help you with more info about the SoM, I've only ever seen the picture in one of the codexes. There is a book called the index Astartes that may contain something about the SoM, but I don't own that one.
- A typical game is in the 1000-2000 range, 1500 or 1750 are considered the most "balanced".
- Concerning armor, I hear everyone going on about mechanised or drop pod armies. Land Raiders are awesome, but I'm no expert on army list design. You better wait for someone elses advice on that.
Finally, that's a very nice paintjob, the weathering in paticular is perfect. Those old platic marines just look so cute too.
I take it you will add the SoM chapter insignia later? otherwise the Rhino in particular looks a bit too green.