We further narrowed down specs for the touchscreen:

1. Should use capacitive, multi-point touch technology.
2. The touchscreen driver IC should be cost-effective, widely available, and have good software support. A GT911 IC from Goodix Technology is a popular touchscreen driver found in many consumer electronic products. It connects over I2C and is supported by mainline Linux. 

Most display panels are sold without touchscreen because touchscreen glass and framing are customized for specific products. There are plenty of suppliers in China that offer customization and assembly of screen parts together. However, they usually prefer to work with high volume orders. We'll most likely buy a touchscreen for initial testing and glue it with a display panel ourselves. Ideally, this should be done in a cleanroom at a factory, but our simplified approach works for fast evaluation.