yes, there is such a thing as too little sex. Just look at Neanderthals, don't see them? Well thats because they all died out.
I had sex with a midget or little person if you like once and she was very interesting so I'll have to say having a little person sexualy is just fine.
Just masturbate to porn and pretend you're the star. Not necessarily. The latest theory is that they never died out, but instead their genes are blended in with many modern humans of today.
There's no evidence whatsoever that a lack of sex leads to anything. Where did you get that notion? As to "mental illness", in today's world, apparently everything leads to mental illness ....even some of the most mundane things. The "civilized" world is a bunch of wussies who can't endure even the slightest inconvience or deprivation. Baron Max