Hi,
I have experience for 15+ years in electronics/embedded development. I have several years of advanced AVR/arduino development, including library development from scratch. Practically all Arduino AVR boards used, like: 2009, 2010, UNO, MEGA, NANO, MICRO, MINI, etc. Several shields used like Ethernet (W5100, ENC28J60, etc.) with various IP protocols implementation, various graphical TFTs with and without touchscreen and various BUS types (parallel, SPI, I2C, etc.), all kinds of sensors and buses, serial and parallel memories, etc.
I have completed previous projects similar to your requirements, using the LUFA code base that is used in the arduino USB interface programmed into "Caterina" (the atmega32u4 arduino bootloader codename). I can easily change the USB hardware IDs to your needs. Can also disable serial interface that can be disabled forever (its support not compiled) or its enabled/disabled state by reading a dedicated pin at power-up.
I will use an arduino leonardo and/or micro that both have the atmega32u4.
The project will be with a fixed price of 200 USD. I will set maximum 15 days time for project completion to accommodate for some problems that are usual to appear with compiling different versions of the bootloaders... I will probably don't need all that time to complete the project, but the total project hours will reflect the 200 USD cost ($11.22 USD/Hr, 9 Hr/week, 2 weeks).
If you are interested in my bid, feel free to contact me.
Regards,
Carlos.