Sorry if I start a thread but I have three quick Q's on buying a J ticket flying with QR in december

If I buy a ticket -

a) Am I guarenteed Tier Points as I will be travelling in December? It makes no difference purchasing now or after QR are officially in Oneworld - is this correct? I read somewhere that the booking classes will change - will that affect anything?

b) I see in the booking process that you can indicate your BA exec number. I should insert it immediately in the booking?

c) IF a "double avios" for booking with QR as a new Oneworld member comes around will previous bookings be valid? What was this like in the past (with MH)?

My main concern are the Tier Points

Many thanks, ^