Since you have a good size tank, it would make sense to start with good size (young adult) silver dollars. In that manner, your 6-8”pbsss would be unlikely to eat them. Particularly since the pbsss is already in the tank.
In your other post you spoke of wide bar dollars. Here you just talk about SDs. Wide bars get much Larger and heftier than smaller SDs, such as Metynnis spp.
Regarding SD growth rates (all of them) - Relatively fast at first, then quite slow, and mostly in heft, not actual size. By the end of their third-fourth year they would have reached somewhere close to full size, and would slow down. And they can live several decades!!! If in good conditions.
I have not kept pbsss but I know the size of prey they will attempt to eat. Thus, I suggest large dollars, or be prepared to loose them, and potentially loose the bass who tried to eat too large a dollar. Also, dollars like to live in groups, otherwise will be very shy.
Good luck, and please post pictures!