FIM GALSync 2 Forests 5 domains

I have been tasked with implementing a GALSync solution and have gone with FIM

Im wondering if the following is possible

Setup is 2 Forests  - 2 Exchange org - Forest 1 has 1 domain and Forest 2 has 5 domains

Currently in Forest 2 they share the same GAL as they are all part of the one exchange org so inter sharing isnt an issue

Am I right in thinking that I need to setup a 2 way sync from Forest 1 to 1 domain in Forest 2 , then 4 1-way syncs from the other domains in Forest 2 to Forest 1

If so how do you set up the 1 way sync ? or any better suggestions

Thanks