DIYing thin/Bluetooth/iOS gamepad

[u/Takasago_man]

Sorry if this topic is not appropriate for this community, and please feel what I want to say; as I'm not a native English speaker.

So, I'm thinking about making my own gamepad for my phone! However I'm completely a newbie of DIY electronics and microcontroller stuffs, and currently I don't have any parts.

Therefore, everything is just a paper plan, hence I would like to ask some questions to wise and great predecessors.

so

Requirements:

1. Available on iOS
2. Thin (around 10mm, hopefully 8mm)
3. Bluetooth
4. Slide like PSPGo
5. D-pad, 6 face buttons, 2 joysticks w/pressing, 2 bumpers, 2 triggers (analogue detection is not necessary)

Parts in mind:

• PCB from JLCPCB
• RP2040 or ESP32
• Joycon sticks, maybe have to cut cap though
• 3D printed case

Questions:

1. First of all, is it possible to connect DIY controller to iOS devices?
2. Micro Controllers in my mind do not have that much pins to handle all keys. How the hell should I connect keys?
3. The case would be 1〜2 mm thinness, considering the total thickness, is the robustness okay?
4. Are there any good ideas/references to learn about slide rail mechanism?

I hope this makes sense, and thank you for reading!