We purchased ours on Craigslist as well. It converts to a toddler bed but we got a toddler bed from a friend and are going to use the crib for this baby. He's not doing bad changing but I can't keep him in it lol. It's fun and exciting though.
I'm 24 weeks now with my first child and we just bought a used crib on Craigslist last weekend. If you're going with preowned, you've got to just buy it when you see the one you want.
Like Louella13, I plan to use a pack and play that has a newborn sleeper feature on top at firsthe in our bedroom. Later Baby Boy will use the crib (which converts to a toddler bed).
Anytime is fine. I used a pack and play for a Lil while since it had the bassinet on top then bought a crib later when I could afford it since the pack and play was a gift. There's no time limit for when to buy as long as your baby is safe.
I'm 25 weeks and 5 days pregnant, I'm due on June 3rd also with my first child I haven't buy a crib yet but I bought some onesies and other baby clothes that she most likely will need when she get here. I'm planning to get mine on April probably close on my 8 month pregnancy :). I hope you having fun. God bless