The front input is limited by the internal Oppo BDT-101 which, like its BDP-103 and 105 siblings, only supports USB 2.0, though you can still connect to a USB 3.0 device. You shouldn’t have any performance issues provided the files on the USB device are not fragmented.
There isn’t really an optimum size. I’ve successfully used devices ranging in size from 8GB to 8TB. Navigating a USB device through the front panel alone can be a bit tedious and you’ll soon see ways to develop a folder structure that will make browsing easier. Navigation using the Media Control app is considerably better and provides greatly enhanced access to the metadata encoded in your files.
Enjoy your DMP - it is an excellent audio player as documented and an extremely versatile machine if you’re willing to spend the time to uncover its potential.
Am I to understand you can control the music on the USB thumb drive with a software program called Media Control. Where do I download it and can I put that on a smart phone and select music from a distance?
The unit can handle about any size stick but best if there aren’t too many files. It was always designed as a convenience input for a few tracks. The navigation system is a bit crude and was never though of as well managed directory for big libraries. Again, it’s a convenience input so you can listen to a friend’s CD or files.