When you apply for a nomination, most MOCs will ask you to rank which SA you want. Many candidates will rotate their SA ranking for each MoC. IE...Senator A: USAFA #1. USNA, USMA, USMMA. Sen. B USNA #1. USMA, USAFA, USMMA. Cong: USMA, USNA, USAFA.
USCGA does not require a nom.
If applying to USMMA it is the only SA that will allow you to apply to every congressmen in your state.
What actually will be a factor is how competitive your state is for nominations. Some states the MoCs will talk and spread the wealth, which means 1 nomination is all you will get, they will not submit your name if another MoC submitted you. It is a one SA, one nomination aspect. Other states that dont talk will allow you to have all 3 nominations. Thus, you can have a nom from Sen. A to USAFA. Sen. B to USNA. Your Congressmen to USMA. And every Congressmen in the state to USMMA.
You need to be careful, because if you don't want to go to a certain SA, than don't put it on your list, because every year there are posters here that ask for guidance with if it is possible to get the MoC to change the nomination/