Electronic – use a 4.7uf 50v in place of a 4.7uf 25v

Electrolytic caps have a tolerance of minimum 10% (the good ones), so 5 uF may be anything between 4.5 uF and 5.5 uF. For the 4.7 uF that's between 4.23 uF and 5.17 uF, so both ranges overlap for the most part. If the operation in the extremes would be important a capacitor for that value would have been chosen. So it's safe to say that 4.7 uF is a valid alternative for a 5 uF.

For the voltage 25 V may be OK, since you hardly see more than twice the power supply voltage, unless you're actually building a voltage multiplier (step-up converter of Greinacher circuit, for instance). But 25 V on a 12 V supply leaves very little headroom, so I would use 35 V at least.

Under full load you're close to 40V peak- you need to allow for high mains voltage and transformer regulation (voltage will rise under light load).

50V should just be okay if transformer regulation is good (usually is for larger transformers). Elna is a good brand.