Hi Kwred,
You should not need to have any data active to receive text messages. However in some cases if the end person is trying to send you a message and it is sent as an MMS, or they have iMessage, it will fail until you turn your data back on. iMessage will attempt to resend a message as text if the orginial message fails.
If you leave your data on, you should not have to worry about going over your data plan. However keep in mind that if you have an email account, or any apps that sync data, such as Messaging Apps (GroupMe, Whatsapp, etc), it will use some data. If you have background data disabled that will keep your data down.