Bismillah

Thank you for your question. Istekhara doesnt have codified rules as it is one of the occult sciences. Rather, it has recommendations for best practice.

When istekhara is performed with the Qur'an or other means it is usually to clarify a situation and so if there are multiple matters that confuse the result of the istekhara then it would be wise to separate the matters and take separate istekharas for each. If there are lots of factors that a person wants to include in the intention and doesn't want to specify each one, but then uses a question that incorporates all of them while leaving the result of the istekhara clear that would be alright.

May you always be successful