Yes, Sony NS-WS623 is meant for the rough usage and it is both - waterproof and dustproof.
Yes, Sony NS-WS623 does have NFC connectivity option.
Connect the USB cable (supplied) to the USB cradle (supplied). Then, attach the Walkman to the USB cradle.
Make sure to connect the terminals ( 1 and 2 ).
Sony WS623 comes with LED indicator. If it is not fully charged and require charging - it will show orange light and when it is fully charged - it will show green light.
Yes, you can connect it with phone and talk and can use as a normal Bluetooth headset.