Hi, we’re about to start using our emonTx V3 in our offices. We need to measure TWO separate three-phase circuits and collect data in order to have our electrical heating system under control.
So I’m thinking of buying one more emonTx V3 but I’m not sure if I can send data from two emonTx to one Raspberry-based emonBase for further delivery (MQTT) or if I need two bases. Any experience on this?
I have in total 4 emonTX sending to my rasp emonbase, it handles it nicely. And as an extra it also handles an emonth 
Although both emonTx’s use the same radio channel, and there is therefore a slight risk that both will transmit their data at the same time and hence both sets of data might be corrupted, the risk of this is very slight. Therefore, as Eric says, you should be OK with both transmitting to a single emonBase.
Remember that the default sketch is for a single-phase supply, so you will need to download the 3-phase sketch to each emonTx.
The 3 phase sketch does not permit pulse counting if that is important.
Using ESP8266 Huzzah wi-fi modules may avoid radio signals clashing - but others are I’m sure more qualfied to comment.
The 3 phase sketch does not permit include pulse counting. It can be added if desired, it might only disturb the timing a little as a pulse is processed, if that coincides with the sampling period.
I posted how to do that only recently - a search should find the relevant thread.