best system is:_
the one that is available to you,
at a cost you are prepared to pay
provides the facilities and capablities you need
is one that either you know already, are prepared to learn, and or have adequate support to resolve any technical issues
meets your user requirements....
what is 'right' for one perosn/organisation isn't neccesarily 'right' for another organsiation
selecting, then sizing the correct db server is fraught with so many issues.
as a truism, virtually any db storage mechanism can support waht you have described so far, ranging from mainframes (do they still exists ),some humungous server farm down to the humble Pi or simialr credit card sized devices. there is not enough detail, not enough practical information to make any sggestion.
there is a mix of service provider with server.
MySQL will porbably be perfectly good enough, whether you decide to run that on a Pi, an ISP or you own dedicated hardware is your call.
I doubt howver phpMyAdmin will do the data capture, graphing and so on... phpMyAdmin is great for as its name suggest MySQL admin, but not a lot else....
I'd rather be riding on the Tiger 800 or the Norton