1. “WILL THE freight rate change if I place orders next month.” Use “will” because you are talking about the future and about a hypothetical. Use “the” in front of “freight rate.”
2. This sentence is good.
3. “WILL THERE BE ANY IMPACT if I place the order next month.” Again, use “will” because you are talking about a future hypothetical. I think “impact” is a better verb for this sentence.