What is the difference between GPS and GNSS?
GPS is a (form of) GNSS, see below (fragment of this link).

GNSS

GNSS stands for Global Navigation Satellite System, and is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. This term includes e.g. the GPS, GLONASS, Galileo, Beidou and other regional systems. GNSS is a term used worldwide The advantage to having access to multiple satellites is accuracy, redundancy and availability at all times.  Though satellite systems don't often fail, if one fails GNSS receivers can pick up signals from other systems.  Also if line of sight is obstructed, having access to multiple satellites is also a benefit.  Common GNSS Systems are GPS, GLONASS, Galileo, Beidou and other regional systems.

GPS

The United States' Global Positioning System (GPS) consists of up to 32 medium Earth orbit satellites in six different orbital planes, with the exact number of satellites varying as older satellites are retired and replaced. Operational since 1978 and globally available since 1994, GPS is currently the world's most utilized satellite navigation system.

BLE

BLE means Bluetooth Low Energy, however Bluetooth and GPS (or GNSS) are two different things. 

GPS module

I don't know what GPS module is best to use. Doing a quick search the module GY-GPS6MV2 shows up often. However, if you found a GNSS module, it will probably support all non-GPS systems too.