Modify existing EA for MT4 and creating dll file with protection.

I have EA which I would like to modify, mainly simplify code, erase function which I don`t use and after that I would like to move main EA code to dll function. i want the dll developed through a free (as in beer) compiler. microsoft free vc is ok. i will give the developer the mt4 source of the robot and he must put all of the mt4 code inside the C dll. the final ea will be as small as possible (ideally, just public variables passed to the dll). the developer should be able to provide me also the directions to download and install the free compiler by myself, with all settings to have a stripped dll without debugging (and decompiler) infos. this is because the final compilation of the dll will be done by myself (with proper parameters inserted by me). i chose C/C++ instead of visual basic because i want the smallest dll. if you can give me a better idea (easy to find free dll compiler producing small and difficult to decompile dll), i will agree. because the ea must work only for a given account number or serial number, a hard-to-unlock system is also welcome.