I am sure a man of your capabilities would get it right.
For general information;
It is really quite simple, just a matter of adding up all the amps of the units on a circuit, so simple example would be headlights, dip. two x 55what is 120 watts (plus 10W for dash and main beam warning lights), divided by 12 is 10Amps so a 10 amp fuse/cable would be the minimum. and I always add at least 10% so I would go 16.5A for the one up to fuse and wire. From switch to relay to fuses 16A and then drop to 11amp after the split for each light. basically, apart from the heavy stuff like starter solinoid feed, (11A) and battery/ starter cables (57A) everything else it would be OK to use 11 amp thin wall.
Technical stuff;
All cables are made up of a number of strands. Generally these strands are 0.20mm or 0.30mm diameter. This also give the cross sectional area in sq mm and the continuous current carrying capacity in amps. The breakdown of the cable specification 28/0.30mm, 2mm2, 25amp is as follows: 28 strands of 0.30mm diameter, 2mm2 cross sectional area, 25amp continuous current carrying capacity.
The following equation may prove useful to work out a cable size required : Watts divided by Volts = Amps
Coloured cables. When two colours are given, the first colour is the main colour, the second colour is the 'tracer' (usually two thin traces of colour which run straight down the cable). eg. Black/white has black as the main colour and white as the tracer colour.
And for the yanks;
AWG22 0.50mm2
AWG20 0.50mm2
AWG18 1.00mm2
AWG16 1.50mm2
AWG14 2.50mm2
AWG12 4.00mm2
AWG10 6.00mm2
AWG8 10.00mm2
AWG6 16.00mm2
AWG4 25.00mm2
AWG2 35.00mm2
AWG1 50.00mm2
AWG2/0 70.00mm2