Piccy,
The PIC16C74 DEMO SCHEMATIC you've posted make use of m@x232A. This device has an higher slew rate, compared to m@x232, supporting up to 200kbps transfer rates.
In case of m@x232A the dual charge pump converter capacitors may be limited to 0.1uF (not polarized ones) still supporting m@x declared speed.
You've to increase their values in the case only your circuit require voltages for ausiliaries circuit (i.e. analog) of +/-10V supplied from m@x232A (from pins 2/6).
In all other cases 0.1uF will suffice. Small multilayer capasitors will be enough and cheaper.
About 10 ohms resistors, your argument about 9V and 900mA would works only if the generator (in our case the tranreceivers in PC) has unlimited current capabilities.
Luckely that's not absolutely true. The tranreceiver in PCs are limited to 20mA and virtually protected from any shorts to ground (short current of 22mA).
So, your question about the use of 10 ohms resistor come back again.
As above said the m@x 232A has an high slew rate. Its value is 30V/us m@x. So, the dv/dt is much higher of simple m@x232. In case of longer wires (let say 30m or longer) you should to consider the wire inductance to be significant. At high slew rate, that is high dv/dt, the wire inductance may have detritement effects on the signal and high ringing effects may be seen especially if the resistance of the cable is low.
To reduce this effects, a dumping resistor to ground, or couples of resistors on TX and RX are normally used. This resistors have the effect to increase the equivalent series resistance of parasitance inductance of the cable.
Obviously this is applied when a sustained trasnfer rate have to be achieved. If you need 9600 bauds, you can forget it.
Hope this help you
james