Your iPad will automatically regulate its battery charging. Unless your iPad or Power Adapter has a fault, you should have no concern for over-charging your iPad. Leaving an iPad connected overnight is common practice - as automatic backup to iCloud (if configured) will occur whilst the iPad is connected to WiFi and Power Adapter - and is locked.
Having an iPad continuously powered for extended periods is also not an issue - as this is commonplace in POS (Point of Sale) and Kiosk applications.
iPad will optimally manage battery charging - and may automatically change its charging strategy by reducing the maximum battery charge level to about 80% of maximum capacity in certain circumstances. This strategy is intended to extend the life of the battery by reducing chemical ageing that occurs when the battery is continuously maintained 100% charge. When a “normal” charge/discharge pattern is resumed, charge to full capacity is restored. This protective behaviour is very unlikely to be triggered when charging overnight.
More information about iPad’s battery management can be found here:
About iPad and iPhone Charge Management Feature – Apple Support
