If you've already got a good chunk of models, getting into 40k
is pretty easy. Pick a points value, play those games till you're comfortable with the rules and mechanics, then expand your points to get new units, new strategies, potentially new tactics, and grow to a size you enjoy playing.
Nothing wrong with playing 1000 point games if that's what you and your gaming friends like. Or going to 5000. Not my cup of tea, I like 1500 to 2000 myself, but that's what I'm used to.
are Astra Militarum... but Guard is good. AM
is just GW
's copyrightable name for them.
You can find the "rules" for the game. Don't buy the rulebook. I thought people were joking when they handed me a pamphlet with the new rules on it. They weren't.