will or be going to?

Dear teachers,

Which form of the future should I use in the following sentences, please?

1) He's pretty sure that he will work / will be working / is going to be working for Jackson & Co. next year as well.

2) His next journey is going to be / will be to Australia.

3) This time he is flying / will fly / is going to fly there from Paris after a meeting with the company's French partner.

4) You’ll see. The moment summer is here, the garden will be / is going to be so / very beautiful!
(which intensifier should be used here, please?)

Regards