I think the technical logics of NR sidelink is almost same as LTE sidelink. That is to develop a full stack protocol that enable direct communication between UEs without getting any cellular network involved. In LTE, it was designed to use UL waveform in both direction (i.e, Tx and Rx) meaning that we need to develop additional stacks on UE side to receive and process 'UL-like waveform (SC-FDMA)'. In case of NR, the scope of new development would not be as much as LTE since fundamentals of UL wave and DL waveform is same (i.e, OFDMA). But some degree of PHY modification would still be required.   

Completely new set of physical channels are specified as shown below. One thing to notice is that both UE in Sidelink transmit SSB and both UE schedules its own physical layer data. It implies that UE has basic component of gNB capability.

The numerologies supported by Sidelink is same as in regular NR numerology as shown below.

Reference :

[1] The 5G Evolution:3GPP Releases 16-17 (5G Americas)