The first criteria is how much voltage the diodes need to block. Above a certain voltage (the breakdown voltage) the diode will conduct large current in the reverse direction (destroying itself and probably another diode that is conducting in the forward direction (by overcurrent since the two will be in series across the mains).
Since the peak voltage on a 220V RMS mains is \$220\sqrt 2\$ = 311V and the 1N4007 is rated at 1kV PIV (Peak inverse voltage) that would seem to be plenty of margin.
You should also consider transients from other things that may be connected to the mains- for example if you had a motor and opened the connection to the motor and bridge, the inductive energy in the motor would cause a voltage spike that could exceed 1kV. In such cases a varistor across the input of the bridge can absorb moderate occasional spikes. The MOV (rated for 230V RMS) might conduct 25A or 50A at 600V, so provided that kills the spike even a 1N4006 would be okay.
In fact, a 1N4007 will probably be okay without the MOV in many cases. You should have a series fuse before the bridge (and before the MOV if you use one). They both tend to fail short.
simulate this circuit – Schematic created using CircuitLab
To me, Kirchoff's Laws are scientific wording of what should be common-sense observations of electric circuits. Unfortunately, common sense isn't as common as we might like.
KVL says that the total of the voltage drops in a circuit must equal the supplied voltage. If that was not true, we would have some voltage across a wire which would result in approximately infinite current in that wire - but KCL insists that the current is the same at all points in a simple series circuit, so we can't have a huge current at one point in the circuit.
If you connect a device that normally requires 4 volts across a 6 volt battery, sufficient current will flow to make the resulting circuit comply with KVL. The voltage across the "4 volt device" will rise, and the output voltage of the battery will fall (due to a voltage drop across the internal resistance of the battery) such that the voltage across the battery and the device are equal. This may result in the destruction of the 4 volt device, if it cannot withstand the extra voltage and current.
Regarding your second point: the voltage drop across a resistor will depend on its resistance, and on the current passing through it, in accordance with Ohm's Law.
For your example of a 10 Ohm resistor across a 30 volt supply, the current through the resistor will be 3 amps, and the voltage across the resistor will be 30 volts. If you add a second 10 Ohm resistor in series, the load on the power supply is now 20 Ohms, so, by Ohm's Law, the current through the resistors will be 1.5 amps, and there will be 15 volts dropped across each resistor, for a total voltage drop of 30 volts.
If you put the two 10 Ohm resistors in parallel across the 30 volt supply, each resistor will now see 30 volts, and will each pass 3 Amps, so the supply will have to supply 6 Amps.
Best Answer
There is a voltage drop. Part of designing a distribution network is to ensure the voltage drop is within a tolerable range, at the maximum expected load.
Let's consider a simplified example.
Suppose that your house power supply is 240 VAC nominal, delivered over a 10mm² two-core cable (single phase power supply.) Your maximum demand is 20 amps. We want no more than 5% voltage drop. What is the maximum length of the supply cable?
Looking up Australian Standard AS3008.1.1:2009 Electrical Installations - Selection of Cables we find some useful tables giving the resistance of various kinds of cable.
Table 34 tells us that 10mm² conductor has a resistance of 2.23 Ω/km at 75° C.
The voltage drop on the cable is given by: 20 amps × 2 ways × 2.23 Ω/km × length (km). The permissible voltage drop is 5% of 240 VAC = 12 V. We can work out that the maximum cable length is 135 metres.
To answer the second part of your question - "how are all the houses on the same transformer getting the same voltage" - the houses are all getting slightly different voltages. However, so long as they are all getting a voltage "close enough" to the nominal voltage, there is no problem.