Ideal voltage for 12 V system, particularly with a mix of DC motors and other loads
Power consumed for most of the loads you describe will be given by \$ P = \frac {V^2} R \$ so increasing voltage by, for example, 10% from 12 V to 13.2 V will cause the power consumed to increase to 1.12 = 1.21 times the 12 V value. This will raise the operating temperature and a standard rule of thumb is that the expected life of the devices will halve for every 10°C.
Most devices designed for automotive use will probably be OK at 14 V as that's the typical alternator output when the engine speed is, say, at double idling speed.
Devices with switched mode power-supplies (SMPS) will accomodate a range of input voltages and output a stable specified voltage.
So, I'm afraid, it's up to you!