Should I go to war

State of Person on White Giant. Built up my population to 15.7 million. Still got beginner's income booster. Haven't got rid of any units I started the game with.

Trying to decide if it is now the appropriate time to takeover a neighbouring non-President country either to take their stuff or to run as a vassal.

Can anyone offer advice on if now is a good time to start playing the war game?

If you are a new player with only one country, the tutorial will help you do a war to take the 2nd country. You can do this without playing the war game. A free member can have a maximum of 2 countries without necessarily playing the war game. If your starting country is developing well and you feel comfortable with the economic side of the game, go for the 2nd country.