Don't replace your starter unless it's very weak. Even then you might be able to take it apart and clean it.
How does your engine run once started?
You should also check the following:
1. Plugs and wires
2. Vacuum leaks
3. Air/fuel mixture (it might be too rich since you have black smoke coming out once started)
4. Temperature sensor and cold start valve
5. Fuel distributor check for internal leaks (fuel pressure drop)

Good luck.