1) Yes. x264 includes the automatically. Its an SEI slice, and you can throw it away if you want.
2) set i_slice_max_size = 1390
3) Take a look at x264_param_t in x264.h. The settings are fairly self explanatory. As for setting the profile and preset call int x264_param_apply_profile( x264_param_t *, const char *profile )
and int x264_param_default_preset( x264_param_t *, const char *preset, const char *tune )
4) Yes, it is true, I want lying when I said that. Look online/on stack overflow there are a million resources on compiling ffmpeg. In fact if you compiled x264 with avcodec support you already have it on your system.
5) Yes!, you should be a good stack overflow citizen and up vote and accept answers form people who donate there free time and knowledge (which takes years to acquire) to helping you.