It depends what your macros would be like as to what I would recommend. My
converter code supports up to 5 keys, and macros by defining them a config file. Or you could set it to output, say, F13 to F16 and then use something like Autohotkey to provide macros. My code isn't open source, if you need/want that there's hasu's extensive
TMK keyboard collection. Macros that involve sequences of
keys work well done in the Teensy firmware, whereas those that involve sequences of
characters are better to do using software on the host. Also, it's easier to change a macro on the host, or implement a record/replay function.