How did you handle preschool?

Ellie
I'm currently shopping around to send my 3.5 year old to preschool. I am a stay at home mom to my soon to be three children aged 0-3.5. I don't need full time preschool 8-3:30 M-F for my son (because I stay home and it's crazy expensive.) However, I do want to socialize him and get him prepped for kindergarten. I feel like full time preschool would be too much for him to handle just starting out. I am hoping to find someplace that offers three days a week for maybe four hours a day but then I'm just not sure if that's enough. 
SO:
For those of you who have gone through this, what worked for you? Was full time too much? Was part time preschool not enough? I want to get my money's worth without overloading my child.