If you say, "Hit me up with the plan," you are asking somebody else to give you details about a later plan. When you say, "Hit me up for the plan," you are saying that you have the details about the plan, and they should come to you to for the details. "Hit me up" is slang, usually meaning, "contact me" (phone call, text, etc.).

"hit (someone) (up) FOR something" is a well-known expression which means to ask somebody for something. "I ran out of money. Can you hit me up for twenty dollars until payday?" = Can you give me twenty dollars..... "Since you're going to town anyway, I thought I'd hit you up for a ride." = I thought I'd ask you to give me a ride. As far as I know, "hit (someone) up WITH something" isn't a fixed expression, and I'm really not sure what it means. However, just reading it, it appears to mean that a person has already gotten the thing he wanted. In other words, "hit me up for" describes the asking. "hit me up with" describes the actual obtaining.