I am sorry everyone. I found the answer myself. I just needed to take the booking one step further and it gave me the choices for seat selection, except for the outbound I received a message that the flight was filling up and they would allocate seats.
There is 3 of us, 2 adults and our son, 6 years old. What are the chances of being able to sit together?
The question with regards to what kind of aircraft also takes care of itself when seeing the seat map.
If seating is 3 - 3 I believe it's an A320 and when it's 2 - 2 it's an Embraer, is that correct?
Any other advice you can give a first time Jetblue flier out of SEA?

How is Long Beach airport? I heard it's quite peaceful which is a nice change from the usual chaos at LAX.