Can iPhone be used with Bluetooth keyboard and mouse? Can an iPhone (mine is 7) be used productively with an external keyboard and mouse -- connected via Bluetooth?

Such peripherals -- combined with a screen-magnifier -- would turn a phone into a decent personal computer...
A Bluetooth keyboard would work with your iPhone. I used an Apple one with my iPhone once. As of mouse I don’t think iOS has support for that (unless some individual app do support it, which almost all apps don’t).