Congrats on the successful keeping. You only lost 3 ATF out of 13, which is far better than my record of ~27 out of ~40, also a mix of GATF and VATF but not all same age and not all in the same tank.
Your tank being bigger has most definitely worked in your favor. Almost all the ATF I lost, I lost in 240 gal, while they did better in 4500 gal. And the vast majority of those I lost were GATF - 10 GATF for every VATF. I am glad to see you and
Red Aimara
have managed to preserve GATF versus VATF.
It's hard to say how many ATF and which species you should retain. I personally would be afraid to upset the apple cart. I think it's a fragile balance. It seems like a mighty rare accomplishment that have achieved already ... so you must have been doing most things right, including the community size and the gender and species ratio, etc. Once you change that, there is no telling what will happen IMHO.
For sure the aggression has been diluted between your ATF. If you reduce their number, the aggression will likely rise for the weakest fish and they likely won't survive, my guess would be. Unless you transfer them into a 30,000 gal pond like that FB guy from Thailand (?) with 5-6 three foot GATF.
Three is a risky number. When my current biggest VATF (2' now) had been about 1'+, there were 3 of them in 4500 gal. The alpha and beta harassed and eventually killed the gamma. They barely commune now, having divided the 4500 gal into two quite distinct territories and fights are not rare.