Avios will be credited to your account automatically in a few days after the flight and contact BA (not QR) if it still hasn't been credited in a week or so.

You don't need to choose between avios and tier points and they will both be credited. Avios is the currency BA uses for redeeming flights, upgrades... Gaining sufficient tier points within a year will bring you to a higher status(bronze, silver, gold).

This means owning a lot of avios won't bring you to a higher status and you can't spend your tier points for redeeming. Check the calculator if you want to find out how many avios and tier points you will earn for each flight.

I have no idea what your flying pattern is but there is no point using BAEC if you are mainly flying on QR. BA offers almost nothing for non full fare QR ticket.

You have to think about which airline(alliance) you usually fly with, how often you fly, short or long haul, the level you will get to with each programme, the efficiency of spending your miles in the future.

Also bear in mind that you will not have much privilege for holding a blue card. So if this is your first time flying with a FF card, I afraid you can't have things like priority boarding, check-in or so...Everything will be perfect once you get to a higher tier.