Which one of these is correct, to speak about a future plan and time?
- I will come to the party if I have time
- I would come to the party if I had time
- I will come to the party if I would have time
Also I'm open to other suggestions :)
Your first sentence is a promise: you tell your hearer that if you have the time you will definitely come.
Your second sentence is a regret: the past-tense forms indicate that the condition is a "counterfactual", a condition contrary to fact, so you cannot come - but if you could you would.
Your third sentence is not idiomatic English. Will and would are never used in a condition (IF) clause in a futurive sense, but only in a volitional sense - that is, when they mean be willing.
If you will do this = "If you are willing to do this" or "If you consent to do this".
If you would do this = "If you were willing to do this" or "If you consented to do this".