The motor speed will not tell you anything useful in a predictive way.
Many machines also use variable speed drives so you don't know what it should be running at, at any particular instant.
Vibration readings are likely to be swamped by cutter vibration & vibration reading also change drastically with speed & load variations as different parts of the mechanics resonate.
Mechanical wear, lack of lubrication, swarf/dust contamination, damaged slideway covers & wipers etc. are all common problems with machine tools but need physical inspection to diagnose - that's the idea of a routine service agreement, eg. a six monthly inspection as Pommie notes.
For example, by the time a slideway demonstrates mechanical symptoms - it starts to seize up due to lack of lube or swarf ingress - you are at the point of a major stripdown to fix it.
Nothing beats the "Mk 1 Eyeball" and simple "feel" of how a machine responds for catching problem.
For data input to a central site, just use a web site with a database and have the sensor devices emulate a form entry, with the data o be added to the database.
The page / php script you post to can be hidden from the normal site pages.
That's how we manage that type of setup (though for somewhat different data).
[Working on machine tool control systems & rebuilds / retrofits for over 35 years].