Yeah, your mod is a great improovement to the...sad to say so, but boring current GC3 version. It is bringing back a feeling of eXploring and eXpanding. Thx for this!
In most cases my setup tends toward max extreme worlds to prevent catch-as-catch-can scenarios. AI is still spreading like hell, so I guess there is still a long road for the devs.
Current games I started, I used beginner level for AI, so they seem quite calm...except the Yor which are OP in my eyes by option to colonize every single ball of dust in space. I cutted them out in the next attempts as neighbouring Yor leads to earliest war ever, no doubt. Wars on beginner level are just easy, while I more concentrated on the other aspects, like economy, gameplay with lower expansion rates aso. Some of my earlier custom races (before mod) offer a quite interesting micro-balancing as they do get the head-start as well. Probably you might consider an option to switch empires on/off head-start, if this could be done.
I think you are in a overall good direction with your balancing and the research patterns as requirement for certain ship modules. Would like to see more of this, as it starts to bring research-ressources-production chains that bring much more flavor. Some 'unique' techs, probably bound toward the 5-6 different tech-trees so it matches custom races design, would be great idea.
Edit: Patch 5.3 breaks the mod, also the new races are limited to one scout even in un-modded game.