I personally think one big shoal would look better than two smaller shoals - but it comes down to what you prefer
If it was my choice i would have 20 rummy noses. I have always found them to shoal very tightly and i think would look spectactular.
Hi
You say that your ammonia levels in your tanks have increased after large water changes. Have you tested your tap water before the water changes? could the water chemistry of your tap water have changed which is having an adverse effect.
just a though
hope he/she pulls through.