Questions on ESF admission

I do not quite understand the system. Appreciate if you can help. thanks.

1. for those who have sibling priority, would buying NR or study in esf
kindergarten further increase the ranking in the queue and higher chance for offer

2. is it hard to buy NR or need to go to secondary market where price is higher?

3. if i dun have any priority, I am just given a number randomly? so by lucky draw to see if i can be chosen for interview? or they have a system to rank u and assign a number in the queue?

thx alot!!