You won't be alone. The server population seems very stable, peaking in the high 800 to low 900 players range every evening (around 8 or 9 EST, I think). There seems to be a steady number of new players who have just heard about the server, people who enjoy leveling slowly, and people starting twinks after reaching 50 on their main.
If you're still not sure, you can watch the front page at
http://www.project1999.org/index.php - in the right sidebar it shows you the current number of people logged in to the p1999 server.
And if you're worried about being alone, start a character that begins in Freeport. With the EC tunnel again the heart of the economy, you will never be alone there
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