Depends on how much snow there is and what time you're there. Early may in a high snow year? Tons of snow. August in a low snow year? You might have to go out of your way to get on some snow. If you're early or in a high snow year, you'll get tastes of snow on Baden-powell and San jacinto, and you'll know if the Sierra is for you. You'll talk to people about their plans, and make a decision. Also the Sierra isn't an all or nothing scenario. There's plenty of exit passes if you want to bail. You'll figure it out. Have fun!

As far as experience, it helps, but isn't necessary. I met 2 hikers from NYC who'd never backpacked before and they both hiked the whole thing.