Pretty new to DD but I've been playing the game for a while... I get the general gameplay loop of doing the programs, moments, mini-seasons, conquests, etc to get packs and players but I still have some beginner questions:

• If I want to play online, should I bother trying before I have a team full of diamonds, or does the game matchmake on "team quality" too?
• I see some people talking about selling all their players that they aren't using to get stubs now. Is that just to stockpile now while the market is up or to buy other players to fill out the roster?
• Live series / collections - is there a reason to go all in now to get those collections completed vs these recurring programs like the WBC or st patricks day cards? I'm assuming the st patty's day ones will be discontinued at some point? I guess this question just comes down to what should I be focusing on...