Ok i know I am new(just got net at home) but been FFF since 8 finished all but 2 3 5 6, but upto finale, I know I will get the same as the eada=terra thread but here we go
First of I think all connecting games are 1000-2000yrs appart

2-4-7
Highwinds, nuff said
1-3-5
All ready said that all odd NES/SNES are game play, so not mush connections except Warrior classes
6-8
Esper and GF similar System, GFs are spiritual Espers, EADA NOT TERRA

1-9
this is the goody for theorists, since 1 has the 8 time loop, its brocken at the end, 9 is the true way through the story+Sarah, BMAge WMage & Thief, my guess RMAGE becomes DRAGOON

unfotunatly I cant connect 10, except to 8, but thats character design