Its hard to say, I have seen it happen where it downloads some, none or all of the previously installed apps, however if you have access to a computer you can log into your Google account and go to the play store and view a list of last installed apps and push install any that are missing to your phone.
You will lose your app data unless its content is saved elsewhere like a cloud or sd card (if the apps supports it)
Any purchased apps will be saved to your account so you will not have to repurchase them.