I just did something similar. I got given my childhood DMG after my mum found it when moving. It would turn on but the screen was broken. I used this screen and this tutorial. You will have to solder the speaker to the new board.
https://funnyplaying.com/products/dmg-retro-pixel-ips-lcd-kit?variant=31899947761725
The screen works great now and is backlit. I also bought a $20 copy of tetris to test it. I then bought a flash cart for it. I have the EZ FLASH jnr. Works fine and it saves games. Has a real time clock which you want for pokemon I think.
The only thing I would say is doing the screen modification was annoying. I went back to funny playing and bought the case and parts they have that fit the screen. It’s in the mail atm.
I also bought a pack of 4 eneloop batteries and a charger. I considered the clean juice xl battery mod but I don’t think I’ll use it that much.
I might do a sound mod to it at some point the headphone jack has a lot of hiss. Might just need to replace some caps.
I have 2 guncon 2’s a crt and a hacked ps2. I really don’t use it enough.