others will disagree, but ACCA guidelines say you need 1" of r/a grill per 2cfm minimum and 1" of 'free' area per 2cfm recommended. Most r/a grilles are about 80% free area.
I like 2 r/a grilles/ducts on 5 ton systems. At least 2.

But as always, you have to deal w/ your specific situation and the practicality/expense of doing by the book.

Doug199 gave you good info. For air filter i use 300 CFM per
sq. ft. of filter. 5 to you are moving about 2000 CFM of air
so your air filter is less than half the size it should be.
Later paulm