Wet food?

I grew up around cats, but we always let them graze-feed from a big bowl of dry food. My first childhood cat turned her nose up at any wet food we tried with her, so she ate dry only. The cats I have now moved out of my mom's house with me, and they've always been on the same dry-only diet. I have heard that it's better to feed them primarily wet food, though, because it's a big water source, so I've recently started getting them some wet food and giving them a little each day.

My main concerns are portion size and schedule. I have no idea how much they SHOULD be eating, because they've always just grazed. I also don't have a consistent work schedule, so it's hard for me to have a regular feeding time for them.

I still have their big bowl of dry food out so I'm not worried about underfeeding them, but I don't want to give them too much wet food and have them throw it up. What portion sizes do you typically use, and what's a healthy ratio of dry to wet?