There is no actual limit. However we do not recommend more than around 50 sensors per modem just for reliability purposes.
The real limit is bandwidth of the wireless frequency, not the actual number of sensors. Also important to keep in mind is this sensor can send vibration data which is pre processed to FFT or it can send raw time domain data. This plays a huge role in how many sensors should be connected to a single modem/receiver. Raw data is huge(up to 20kb) where as FFT data is significantly smaller(less than 300 bytes),
Will you be developing software to parse the data from the sensors? What is the intended use case of your application? ie Where will you be sending the data to?
The Modems are intended to be connected to a local computer. In the case of WiFi or Ethernet this is via Local Area Network. The local computer will need to run a script to parse the data, then convert it to a format the end software(Splunk in this case) can digest.
I would highly recommend investigating the Enterprise Gateway here as it has built in processing/data conversion capabilities as well as WiFi and Ethernet Interfaces: