Yes, or for anyone (like me) who likes to work with hardware themselves. Also maybe to save some money. By using a solderless breadboad, I can rewire it to make any changes to match the final Arduboy version, when the details are made available.
The answer is yes to both questions.
There are slight differences between my system and the Dev Kit:
The Dev Kit runs at 16MHz. Mine runs at 8MHz.
You could use the SparkFun Pro Micro 5V/16MHz version but you would need 5V to 3.3V level shifting logic to drive the display, or use a display module that is 5V tolerant. If @bateske decides to run the final Arduboy at 5V and 16MHz, as he is now planning, I will probably change mine as well.
The SparkFun Pro Micro that I used doesn't bring out pin 12. The Dev Kit uses this pin for the display reset signal. I've currently connected the display reset line to pin 3, and had to make a small change to the Arduboy library to account for this. If you want to run at 5V/16MHz, then in place of the SparkFun Pro Micro you could use an Arduino Leonardo, or Arduino Micro to gain access to pin 12 for better compatibility.
The Dev Kit shorts pins A2 and A3 and wires them both to the speaker. This is not good! You shouldn't short two outputs together. I wire to only one pin at a time, depending on which one the sketch uses.
I believe the Dev Kit runs the processor directly from the coin cell battery, which would be about 3.0V, or at 5V when connected to USB (maybe someone can confirm this?). In my system the processor always runs at 3.3V from a regulator on the Pro Micro board.
The piezo speaker that I used is not the same as the one the Dev Kit uses. It may sound slightly different.
The display module that I used has no CS input. This doesn't affect anything since no other devices are attached to the SPI interface. If you want to make your own system I would get a display that has all the required signals available.
Other than changing the library for the display reset pin, and differences due to clock speed, my system behaves almost exactly as a Dev Kit. You can develop and run Arduboy sketches with it.
The SparkFun Pro Micro that I used is open source. The display is a standard design with a standard SPI interface and there are many different vendors selling versions that would work.
The safest (but expensive) display to use might be one of the ones from Adafruit, either the 0.96" one or the 1.3" one. These are both 5V tolerant and are virtually guaranteed to work.
I'd be happy to tell you where I got the components, or offer alternatives, or tell you if ones you have found will work.
I put the buttons on separate boards because the ones I used didn't plug directly into the breadboard properly. If you used buttons that were breadboard compatible it would make things easier.
The wiring is as follows:
Arduino Pin Display Pin
3 (or 12 if available) Reset
4 D/C (data/command select)
6 SPI CS (chip select) (not used by my display)
15 SCLK SPI SCLK (clock)
16 MOSI SPI Data In
Buttons are normally open push buttons. One side of each button goes to system ground. The other side is wired as follows:
Arduino Pin Button Name
5 D-pad RIGHT
8 D-pad UP
9 D-pad LEFT
10 D-pad DOWN
7 Start (not on the Dev Kit)
RST System Reset (not on the Dev Kit)
I might have buttons A and B reversed. I don't know if it's been decided which is which.
One side goes to system ground. The other side goes to pin A2 or A3 (but not both!). The Dev Kit shorts pins A2 to A3. Don't do this. Use one pin at a time.
The Dev Kit uses the Arduino RXLED pin 17. This is wired to an LED on Pro Micro, Leonardo and Micro boards, so no extra LED is required.
The negative (black) lead of the 3 AA battery pack is connected to ground. The positive lead (red) is connected to the RAW input of the Pro Micro.
The display I used has an on board 3.3V regulator (it's supposed to be 5V tolerant but I investigated and found that it really isn't), so I connected the display's VCC pin directly to battery positive. If the display you use requires 3.3V power, you could get it from the VCC pin of the Pro Micro.
I don't have a power switch. I just remove one of the batteries, or one of the leads, to power the system off. Because of the design of the Pro Micro, you must make sure the batteries are disconnected while connected to the USB port.
If you make a 5V system, you would need to use 4 or 5 AA batteries or some other means to power the Pro Micro. If the display required 3.3V you would have to find a way of providing that as well (plus possibly add external level shifter circuitry to the display signals).
Your English is quite understandable.