To create software module for Raspberry Pi or STM32 microcontroller

I have several modules to be written on both of devices. Device numer one: Rapberry Pi Zero with dedicated 3.5 inch touch screen (480x320 dots). Ethernet interface. Running on OpenWRT linux system. Custom application written in C++ Eclipse IDE. Device number two: custom made electronics with STM32 F4 processor, 2.8 inch Riverdi resistive touch screen (320x240 dots). ethernet interface. Framework created in Ecplise System Workbench for STM32. I have two modules to be written: Number one - create Web Server where it will be possible to customize how main screen on device should look (it shall be possible define background image (upload jpg file to device), shall be possible to create buttons rectangles (also upload jpg file to device)) Pressing on screen where buttons are drawn shall execute function included in software. Module Two. On Web Server LUA script editor. LUA script to be later executed on the same machine. So in short words I want to give user opportunity to write his own code which shall be executed on this device. If it is easier to create separate application running on computer which will be able to send settings to microcontroller then an option is to create such an application instead of WEB serwer based solution. But I prefer to build it on WEB serwer solutions embedded into device. From freelancer accepting a job I am expecting small steps proofing ability to handle cooperation.