When you format each partition with a normal format and not a quick format, you are also scanning the disk for faults. To check for bad sectors you would have to do a thorough scan of the drive.
Many will come on and say you don't need to format but that’s up to you. It's your hard drive and you can do what you want. As to the size of each partition, that depends on your O/S, what you want to store or do on each partition but you will always find that you had made one smaller and that you had made another larger.
4 equal sizes would be about 35Gb each.