looks good to me. Maybe get an empty game cartridge too? But I would also consider skipping the teensy, and wiring the PCB directly to the pi's GPIO's (following the link I posted earlier). But it's up to you, using the teensy will eliminate the single usb port of the pi zero, so if that is okay with you go that route. I prefer to use GPIO controls, and then extend the pi's micro USB to a full size usb out the EXT port, that way you can still connect a keyboard or something if you need, plus it fills a big gap in the case. I didn't see on the list, but if you plan to use a usb hub, then it really doesn't matter, since that will give you the extra USB's.
Also, if you're already buying a bunch of stuff from Handheld legend i'd get the gameboy case from them too, then you won't have to deal with slow ebay shipping. (might cost a few dollars more I guess).
But...... alternatively, you can check out the seller gamerszone on aliexpress, they have pretty good prices, and if you use epacket shipping (select one item with epacket shipping, and then select all others in the cart set to free shipping, they will only make you pay epacket prices once, which is really nice.) it is pretty quick considering it's coming from China, you can get all the buttons, silicone pads, volume wheels, gameboy shells/cartridges, and glass if you need it (only clear ones though, no gameboy zero branded ones like HHL)
https://www.aliexpress.com/store/group/ ... 6517Qdwh8a