Welcome back to the game. I'll offer you my suggestions and input.
I've been thinking about playing warhammer again. I stopped because the store closed down and everyone sold off their army. I found a new group at an other store,so I'm thinking about playing again. But here is the thing I stopped playing in 6th ed, and after watching a few games. I don't know if my old army can even play against some of the crazy now. I'm seeing army's almost getting wiped out and still winning because they can get those "card objectives" easily or at the last second. But I'm just going to look at that like a learning curve, and the one thing that's got me worried is almost all the army's has some kind of forge world in it. I have bit of a bad history with forge world because every time I played against it. It was something that had the rule going for it with a competitive army for just a fun game, and that's what the gaming group looks like.
Don't worry about the edition. I find that 7th is the best the game has ever been but soon we'll be getting 8th edition and it will change everything. Tactical objectives is a great format and one which I prefer although many players seem to find the random element to be unfair for competitive style games. I find such games become more tactical and less about wiping out the enemy. Hopefully they'll remain under 8th but we might see new missions types instead.
As for Forge World, once upon a time FW models were massively overpowered but these days they seem balanced along with everything else. Saying that I haven't played against Titans so I can't say how well or not they balance out.
-Space marine/Blood angels/Space wolves-
I have a bit of everything, but what do I need to add to it, or do I have to pick a chapter and stick with it?
Each of those armies has their own strengths and weaknesses. 7th has an Unbound army building system that lets you play anything you want but you lose out being able to contest objectives. Some players dislike it but if you want a mixed force or want a space marine army that has bits of everything then it's an option to consider.
I've played them before and I like an all vet army with tanks and flyers
They are called Astra Militarum now. Sounds like you have a good start for them.
-Sisters of battle-
Love to start but to much $$$
Hold your wallet tight. Things are pointing to plastic sisters being on the horizon.
Seems to be a easy way back in
They work better as an ally to an Imperial army rather than being played as an army on their own.
No idea where to start, seems like it will be a fun army/
I'd recommend picking up Gathering Storm book 2 and going for a Reborn of Ynnead army. I'm expecting the whole Eldar army to go that way soon anyway.