kavya,
If you're using a car, I'd suggest staying in Monterosso as that has the best parking of the five towns. There's a large lot at the far end of the "new town", close to the water. I don't know what the charges are? As I recall, there are two routes into Monterosso - one into the "old town" and one into the "new town". Be sure to take the "new town" exit (hopefully Roberto will spot this Thread, as he'll be able to provide more specific directions). One important point to note is the you will NOT be able to drive into the town, especially the "old town" which was damaged by flooding in 2011.
I don't know what the current status of parking is in the other four towns. I'm not sure whether the visitor parking has been rebuilt in Vernazza, so that might not be a good choice with a car. There's a large car park near the station in La Spezia, so you could leave the car there and just use the local trains. Having a car in the Cinque Terre is somewhat of an expensive and useless option.
Monterosso is at one end of the C.T., so it would be a great location to take the boat in one direction and then return by train. As you'll be there in the very near future, I'd recommend getting a hotel booking SOON! You might try Villa Adriana, as they have limited parking on-site and they're also not far from the car park mentioned above. You could also check THIS list.
Buon Viaggio!