Thanks for the input, I'm leaning more towards the pair right now because I wouldn't want him alone; having some company is always best right - for better or worse.
IMO silver dollars are a little large for dithers in a 75 gallon, not that they would be cramped, but are pretty sturdy fish and get to 5" so would look too big to shoal well. If you had a proper school it would be too much I think. Try some tetras like diamond or Buenos Aires for dithers.