I have iphone se (about 6 years old). Can I use it with USB C adaptor/lightning cable?
See above question.
See above question.
Yes. They're supposed to be compatible with anything that has a Lightning input port - all the way back to the iPhone 5. Apple's compatibility list includes the 1st generation iPhone SE
Buy USB-C to Lightning Cable (2 m) - Apple
iPhone Models
Any USB-C power adapter will have 5V available, and is supposed to default to 5V first before negotiating operation at a higher voltage if compatible. The electronics in the cable are supposed to know the requirements for the device it's dealing with, although I'm not sure how non-Apple devices with Lightning ports (like some USB power banks) are handled. As long as it's an Apple OEM or MFi cable, you should be fine.
Yes; you can uses any iPhone that has a Lightning connection with either a Lightning to USB cable or a Lightning to USB-C cable.
Yes. They're supposed to be compatible with anything that has a Lightning input port - all the way back to the iPhone 5. Apple's compatibility list includes the 1st generation iPhone SE
Buy USB-C to Lightning Cable (2 m) - Apple
iPhone Models
Any USB-C power adapter will have 5V available, and is supposed to default to 5V first before negotiating operation at a higher voltage if compatible. The electronics in the cable are supposed to know the requirements for the device it's dealing with, although I'm not sure how non-Apple devices with Lightning ports (like some USB power banks) are handled. As long as it's an Apple OEM or MFi cable, you should be fine.
I have iphone se (about 6 years old). Can I use it with USB C adaptor/lightning cable?