Historical Bitcoin full node counts
Everyone that ran a node has/had the ability to record lists of other Bitcoin nodes and their IP address with a "getaddr" request (assuming they allowed incoming connections). I am not aware of a centralized online database of these records dating back more than 1 year: https://bitnodes.21.co/dashboard/?days=365
Yes: https://bitnodes.21.co/nodes/
Some early adopters used real IP addresses and others (including Satoshi) obscured their IPs with Tor, VPNs, or other means.