IPad Questions.
For an IPad, would I have to pay for it monthly like I would for a phone?
Question marked as
Presumably you refer to an Cellular plan for your iPhone - for which you pay monthly.
Purchase of an WiFi+Cellular model iPad does not obligate you to adding a Cellular plan for the iPad. Many users choose a Cellular model iPad for two reasons - one being future flexibility if a cellular connection were needed, but perhaps often because the Cellular models of iPad have GNSS/GPS capabilities and functions that are otherwise absent from the cheaper WiFi Only models.
As for Cellular plans for iPad, many different options are available - including monthly contracts as perhaps used with your iPhone.
Be aware that an iPad, whether a Cellular model or not, is not capable of directly accessing Cellular Voice or SMS/MMS Messaging features. An iPad with either WiFi or Cellular connectivity alone can only access IP-data services. If you have added a DataSIM or activated the eSIM with Cellular plan to a WiFi+Cellular model of iPad, the number associated with the DataSIM/eSIM is only used to identify your account for billing purposes. This number is not (and cannot be) used for making calls or sending messages.
However, when paired with an iPhone, the capabilities of iPad significantly broaden to include access to Cellular Voice and Messaging services of the associated iPhone - relayed to the iPad over WiFi using Apple’s continuity features.
More information about Continuity and the relevant Cellular services can be found here:
Continuity
Use Continuity to connect your Mac, iPhone, iPad, iPod touch and Apple Watch – Apple Support
SMS/MMS Messaging
WiFi Calling
Make a call with Wi-Fi Calling – Apple Support