I'm lost with empirical formulas here, just need the steps here.

but the CsSO4 doesn't seem to be accepted:
It needs to be Cs2SO4
Cs = 1+ and SO4 = 2-
so the Cs has to be multiplies by 2 to equalize the charges.

Another strategy is to use the charge of the + ion as the subscript of the - ion and
the charge of the -ion as the subscript of the + ion.

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It doesn't always work. If one charge is a multiple of the other you have to reduce the ratio to lowest terms, at least for inorganic compounds.
Example Pb4+ and O2-.
The strategy results in a formula of Pb2O4, but the formula is PbO2.

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with Rb and I you can see they are both univalent
so the formula for the compound is RbI

Cs have charge of 1 and SO4 has charge of 2 so the compound is Cs2SO4

these are the simplest ratios of the elements in the compounds and are the empirical formulas too