In a use case like that, I’d probably only send events to Estimote Cloud when I (a) detect a new visitor (= beacon) came in range of the LTE Beacon (an “enter” event) and (b) when I stop detecting that visitor for, say, 1 minute (= they left the range = an “exit” event).
This way, you can keep the real-time’iness, but are a little more efficient with the requests, since you only report changes, instead of constantly reporting the entire state of the system.
Also, if real-time’iness is what you want, having the LTE Beacon plugged in will probably be a requirement. When on battery power, the LTE radio’s default state is to sleep, which means there might be a minute or two of delay to wake it up, log into the network, and send data. When connected to USB power, the LTE radio will stay logged in to the network. (Note that this behavior is something I’d consider an implementation detail, so we may change this in the future.)
And how long in distance, can LTE-Beacons detects the beacon?
This mostly depends on the beacon and its broadcasting power/range. Proximity Beacons have something around 70–100 m in an open field when set to max broadcasting power of +4 dBm. Indoors, this number will go down.