Definitely measuring and diluting concentrate is easier and should in general produce the same final solution. That is, if the concentrate doesn't get past solubility limits.
And yes, your approach to calculation looks more or less correct in terms of the logic involved, however, it can be done much easier. You don't need to convert to moles. You know the final solution has to contain 1.1 g NaCl per 5 gal of water, right? So if you manage to dissolve 11 g in 100 mL of water and then measure 10 mL of that, it contains exactly the amount you need. See the difference?