Yes, Nokia 5. 1 does support OTG.
No. Nokia 5.1 has 2 dedicated slots for the sim cards and 1 dedicated slot for the MicroSD card. You can use up to a 128GB memory card in Nokia 5.1.
Nokia 5.1 comes with 5V/2A charger output. It is quite fast.
Nokia 5.1 has a single channel 3GB RAM. The RAM frequency is 933 MHz.