[@Vigfast]The thing is, speaking realistically, mechs would be developed ultimately to mimic human movement. Its the natural progression. Gundam has more 'human' mecha because gundam takes place quite a while after the mecha have become mainstream, and therefore sufficiently advanced at this point to mimic humanity, because the first gundam was not anywhere near as mobile or speak. 

more of a personal opinion now, but id honestly prefer piloting something exactly like me, than feeling like I am actually controlling a giant stiff hunk of metal. It would be less responsive, and less streamlined or good for open combat to me.

as for 'mods' I can imagine many reasons why operatives would have personalized frames. Funding would be provided by our contractors to use as we see fit as id imagine with the current plot. From there, your character only needs to understand physics and engineering(things they would because they pilot the damn things.) From there its just finding the engineer to install said upgrades.