Icade bartop build - few questions

[Solid_Snake]

I'm trying to make a list of things I need to purchase for my build and have a few questions I hope I can be helped with.

For the screen I will use an Ipad 2 lcd screen with a vga-hdmi controller(with audio as I've read complaints about the Pi's audio).

I have a Raspberry Pi 2 Model B I received as a gift. In the future I'd like to acquire a Pi 4. Will images for Pi 3 + work on my Pi 2? I'm currently looking for a job and that's how most of my day is spent, this project is a side gig to keep me motivated. Ideally I'd build my own library but I don't have time now.

This is what I'm having trouble with : Audio and Internal Electronics.

I know Pi runs 5V, the Ipad requires 12V/4A. I don't know anything about anything regarding electricity other than there are AC and DC classifications. Some people recommend going usb audio but I like the authenticity of having small speakers with an amp. Most 2" to 3" speakers are either 4 or 8 ohms (have no idea what ohms are). I'd like an amp with a knob and bluetooth. I've seen most people use a class D amp I've seen some with out knobs, how is the volume regulated? Any recommendations? What do I need to power the two small speakers?

I'd also like to add led lights for the marquee. I have no idea how to power these as well. Lastly I'd like to add led buttons. Is it possible to make these turn on and off at will? How will these be powered?

To complicate my build more I'd like to have a button that turns it all off and on from a single switch while I'd like to have the option to have an on off switch for the marquee lights and another for the LED lights.

Do I need a dedicated PSU or a will a normal power strip some how modified or tied to a push button work?

I will look for some basic 101 arcade cabinet wiring but in the mean time I'd appreciate it if you fine people can steer me in the right direction.

I'm trying to keep the cost to a minimum as I am unemployed but am open to all suggestions nevertheless.

Thanks!