I am in the process of thinking of a new army as well, but I'll see if I can help you a bit.
For sisters of battle, it's going to be a very exciting release, and the new chapter approved coming out in the next couple of months will have a Beta codex to try out. I highly doubt repressors will be in the book however, as GW and Forge World tend to keep their toys separate. Although, that doesn't mean we won't see a different vehicle. Who knows. I imagine with the Beta Codex, they won't include datatsheets for new units, which might be a surprise when the real book is released.
For Marines, you are under no obligation to play Primaris marines if you don't want. You can also easily play a mixed army, a lot of folks do, and it's supported in the lore.
I don't think we'll see non-primaris marines phased out. Primaris are just an option. I do doubt we'll see many more non-primaris releases though. I think it's safe to assume if it's in the codex now, it'll stay.
Blood Angels, are very similar to the rest of the space marine line. The biggest difference, is in the collection of specific units, like the Death Compant, and Sanguinary Guard. However, as they are marines, you can build your Blood Angels anyway you want.
Prmaris Marines, stand around a head taller than Space Marines, and the shoulder pads and heads are interchangable. Deathwatch use the same shoulder pads for their Space Marines, as their Primaris Marines.
For Chaos, there is a couple new-designed Chaos Space Marines featured in the new Blackstone Fortress game, and speculation says we might see new Chaos Marines released in the next little while, along with a Plastic Abbadon. Also, some folks are equally saying we might get an Emperors Children and/or World Eaters book/Releases soon as well. But, that's all speculation, so it's hard to tell.
Death Guard, and Thousand Sons new plastic lines are both similar quality to the Primaris Marines, but not as tall.
For where the community went, it's pretty much all gone to Facebook groups. People don't care much for fourms anymore.
Anyway, I hope that helps a bit, and if you have some specific questions, feel free to ask.