Ok, would have been easier to have the full configuration of R6 and R8 to see what's going on there and not a partial one of a router that works. Anyway.
Regarding the connection errors between R6 and R8: In general, there is not much that can go wrong with LDP session setup. LDP uses UDP/TCP port 646, so first of all make sure that is not blocked by firewall filters on the physical interfaces or lo0. Second, check the transport address.
As of the missing routes in inet.3: LDP is not a routing protocol, but only a label binding protocol. You did not mention the configuration of an IGP (OSPF or IS-IS), but that would be a prerequisite of populating the inet.3.