Modifying vintage toy: Adding sound, and automatic turn off

[ampliwire]

Greatings everyone!
I recently started a new project. I'm going to modify a vintage toy powered by two D batteries in series.
The plan is to add ''sound'', and automatic switch off.

Delay circuit:
As of today the unit stays on till you turn it off, but I would prefer if it stopped after 12 secounds. I was woundering if it is possible to add a relay delay circuit, but the voltage from the batteries is only 3V..
I briefly read a bit about 555 timers, but I didn't quite understand if this is something I could use.

The toy has a standard SPST switch, but I'm soldering a spring loaded one instead, so I can use one of the relay poles as a holding circuit. (that is if I could use a relay of course)

The talking function:
So I'll use a tiny D class amplifier, and a tiny speaker. But I don't know what to use as a file source, I do believe arduino could be usefull for this? Never used one before, but I hope it's not too hard to program.
The functions I need is for it to play the sound file when voltage is applied. I will add several files so it need to have a random function as well. This is because I don't want it to play the same file, everytime I turn it on. Later I was thinking of maybe just using a old .mp3 player, but they don't come with automatic turn on when voltage is applied..

Also I'd like to do the mod as cheap, and small as possible because of space issues.

Anyone have a solution?

[0xdeadbeef]

Dunno if that helps but for a fun robot project I used one of these ultra-cheap "DF player mini" clones from China. They sell for 1-3€ from China.
Mine had a YX5200 chip on it which can be controlled through UART and has a 3W amplifier integrated. But I think there are derivatives with other chips.
I chose the YX5200 as it can be controlled through UART, but there are also four input pins to control it. Didn't test it, but I understand you could use four pins to control it.
Anyway, also given that the XY5200 needs some time to boot/scan, I guess for your purpose, there are other MP3 chips/boards which might work better.
E.g. there's module called BY8001 which has  five IO pins to control playback. Can't really tell if it would play track 1 if you tied IO1 to ground, but it's worth a try.
Otherwise you'd need at least a little timer and a transistor to trigger the pin for a certain time. Can't tell about boot time though.