Mod secondary base value

No and no, all RNG

Max value I think yes. There's a max for every time it can be upped, so max would be 5*up value (4 from levelling the mod and the 5th for its starting value). For anything less than a yellow mod, reduce it by 1 per rarity, because you necessarily get 4 secondary stats on a mod. So a white mod will get 4 different new stats, green 3 different new and one upgrade of an existing one, etc.

I don't know what the exact values are. I think it's a max of 5 speed per upgrade of a 5dot mod, so incredibly lucky people have 25 speed secondary mods.

Thinking about it, that's actually completely ridiculous. You can get almost as much speed as a secondary stat as you can on a 5dot speed arrow. Mods need rethinking.

1. a mod with 1 secondary stat at lvl 1 will improve that secondary stat once (Guaranteed!)
2. a mod with 2 secondary stats at lvl 1 will have 2 improvements at lvl 4 and 6. RNG decides which of the 2 base stats will improve.
3. a mod with 3 secondary stats at lvl 1 will have 3 improvements at lvl 4, 6 and 9. RNG decides which of the 3 base stats will improve.
4. a mod with 4 secondary stats at lvl 1 will have 4 improvements at lvl 4, 6, 9 and 12. RNG decides which of the 4 base stats will improve.



https://forums.galaxy-of-heroes.starwars.ea.com/discussion/59755/massive-mods-guide/p1

Thanks for answering , nice explanation and for ur link i've read it before but some points about these values were still weird for me :)