Indeed they do, but the default for the emoni/emonBase is 5, for the emonTx’s the default is 15, with 16 available for the second one.
They are about 1 m, there’s an article in ‘Learn’ showing the best way to extend them.
Do you want to measure the temperature? I don’t know!
You need two, one for each emonTx (ideally). With the a.c. adapter, the emonTx can calculate real power (which is what your tariff meter reads). Without it, it has to guess the voltage, which inevitably leads to one approximation, and it can only give you apparent power anyway, which is a second approximation. That might not be too bad for the inverters, but the house power is likely to have a significant error. Besides all that, you need either a 5 V d.c. supply OR the a.c. adapter for the emonTx’s, so there’s no significant saving - but see below.
The voltage around your house should not vary too much except when you have a heavily loaded long circuit. The emonPi (if you have one) won’t need an a.c. adapter until you add c.t’s (for the same reasons) but it will in any case need a 5 V d.c. USB power supply.
(So at your consumer unit, you’ll need two sockets, possibly three, and one, possibly two, by the inverters.)
The 433 MHz ISM Band radio is a significantly lower frequency than Wi-Fi. So it should penetrate the house somewhat better. (Is it brick or stone?) The emonBase/emonPi has both Wi-Fi and Ethernet. If the emonTx is right next to the emonBase/emonPi, it might have a problem because the signal is too strong. The one in the loft can have the power turned up (you’ll need to add a programmer, and be able to take a laptop to it to do that), but unless you’ve not got wooden floors, the signal is less likely to be hampered coming down than it would be going around on the same floor.
If you’re adding more than a couple of temperature sensors, or you turn the transmitter power up, you’re likely to need a 5 V d.c supply to the emonTx as well as the a.c. adapter.