How many displays can I plug into MacBook Pro (13-inch, 2017, Two Thunderbolt 3 ports)
You can plug in a maximum of two monitors

The technical specifications gives you detailed info about what your specific model’s capabilities are.  In this case, your model MacBook - 2017 13 inch MacBook Pro - has enough bandwidth to support two monitors at 4K or less or just one monitor at 5K.

The Thunderbolt information page gives you a generalized perspective of Thunderbolt’s capabilities.