When you're ready to start hatching, I recommend at least 2 (but no more than 4) around the same time. They don't eat often and milk only lasts about 2 hours if you're lucky and use preserving salts. A normal female gives 5 milk at a time. Good luck!!
I got a level 150 lightning egg and I was so excited to hatch the egg...that when I went to put the egg down I accidentally ate it instead. :( ps4 users: R2 ISN'T GONNA DROP THE EGG YOU'RE GONNA EAT IT LIKE ANY OTHER EGG. REMEMBER THIS. LOGIC BEFORE EXCITMENT.