1) Yes
2)
Yes if you want to and you are short on cash you can wait.
The thing is if you won't upgrade you stadium and when you have finished upgrading every other thing for that stadium level then you won't be able to upgrade any further as the upgrade are locked by Level. You have to upgrade everything on each level to unlock further upgrades.
So either you upgrade your stadium or you won't have anything to upgrade. I will advice your to upgrade Youth Academy ASAP.
The more slots you open in Youth Academy the more player you can have. Selling these young players generates a lot money which is important and scarce at low Level.