I agree with "alms," but why did you choose "shall" over "will"? To me, in this context, "shall" has a decree connotation, while "will" has a prediction connotation. The verse seems to fit the latter mood more.
You have a point. There are no commands here.
Why not "if you are believers"? We are really translating the Arabic "if" (one of three versions itha, en or laww depending on the level of doubt) rather than the verb being used. In this case, en is used which is the middle level, and I feel that this level of doubt is already reflected by having the if statement at the tail of the sentence.
Only reason is to translate
كنتم. Literally, the phrase means, "if you were believers." That's an Arabic style for saying, "if you really are believers." So, adding "should" approximates that meaning. But, I'm open to suggestions.