Mod secondary base value

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.