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I can answer the first - the emonTH calls in every minute by default, but it's extremely easy to change. You'll need to modify the firmware on your emonTH devices anyway to assign them all unique node IDs.

I haven't tried anything extreme range-wise, but I do have an emonTH calling in through an external wall (brick double leaf) and around 20 feet or so of air, and another from loft to ground floor (through suspended timber).

The radio range of the RFM12B module is allegedly about 100 m unobstructed. We have seen reports of some people achieving ranges approaching that in real life, and others who struggle to achieve a range of more than a few metres (though we often have no detailed information about the physical conditions, nor of sources of interference that might be affecting the performance. You can improve the range by slowing the data bit rate.
See http://jeelabs.org/2011/05/15/rfm12b-range-testing/

The effective resolution of any of the ports is around 1% for reasonable accuracy. The ADC is 10 bit, and you need a reasonable representation of the input wave to get be able to calculate the rms value, so you need a few bits for that. You can increase the input sensitivity by increasing the value of the burden resistor, provided of course you remain within the VA rating of the c.t.

You can extract data from emonCMS - see the Help.

I believe you can add WiFi, but it's not offered. The additional current required would likely mean that you would need an external power supply for the emonTx V3. There is a suitable connector available from the shop, but not the antenna (AFAIK).

You are using "contactor" in a totally different sense to how I understand it, so I cannot help you there.

Thank you for the answers, emonTH rate 1min is what I need.

So I will need to always reload a new firmware to specify an ID each time I need to add an emonTH (expect the first one) as they are all provided with same ID ?

I don't need the value to be reliable against reality I only need to be able to be precise enought distinguish the 50mA variation between boilier using pump only or pump + gaz.

Using a standard Multimeter with poweramp clamp it show me 500mA pump only and 550mA pump+gaz (220v).

For contactor the DS1401 is a 1-Wire component that purpose is only to answer with its ID number if some general ID request is send over 1-Wire network. 

I use ILS contactors on doors and windows and put a DS1401 behind each one, if magnet is glued then DS1401 will be present on 1-Wire cable, if magnet is not glued then DS1401 will not answer any ID broadcast request.

So I will need to always reload a new firmware to specify an ID each time I need to add an emonTH (expect the first one) as they are all provided with same ID ?

That is correct.

OK and what about the PowerAmp clamp ? will emonTx be able to show me 50mA variation if plugged into port 4 ? 

50mA at 240V is 12 Watts. 

My PV Router sketches can certainly detect this change in energy flow.  This is when set up for a full-scale of around 4 kW which I think is how port 4 on the emonTx V3 is intended to be used. 

OK, now one more question, I am wondering which emonTX too choose, I see that there are V2 and V3 and have not found any compare article that could help me make my choice.

But are there not photographs on the shop website? V2 uses through-hole components that you assemble yourself, V3 uses surface mount and comes largely ready-assembled. You add the optional bits. The V3 performs slightly better at low currents.