Edge design is thoroughly discussed in the Reference Design found here: VMware® NSX-T Reference Design
Ultimate goal which is possible in 2.5 is to have a single NVDS for both overlay and VLAN. This is the simplest and recommended design. I always use a single NVDS for host transport nodes and for Edge I do the same on 2.5 or use 3 NVDS (1 overlay + 2 VLAN) in NSX-T 2.4.
Regarding connection of Edge fastpath interfaces you have to think that this is actually the uplink of a NVDS that resides inside the Edge itself. If it is an edge VM it can be connected either to the hosts vDS or NVDS in a collapsed design. Either way the port group (or segment) of the host just needs to be a trunk so it can correctly tag traffic going to physical network and carry both the TEP VLAN tag or T0 uplink tag.