Nokia 5.1 has a 3GB LPDDR3 type RAM. It is a single channel.
Yes, Nokia 5.1 is a VoLTE mobile phone.
Nokia 5.1 comes with 5V/2A charger output. It is quite fast.
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.