No, it doesnt not affect your ability to perform as usual in sexual intercourse at all
If he has a testicle, there will be sperm.
Yes, as long as the testicle is functioning properly then you can reproduce with one testicle.
Not if only one testicle is removed. You can produce sperm just fine with only one testicle
Nope, each testicle both produces and stores the sperm.
The overall Count will be a bit lower, but if that testicle is healthy, the man will still be fertile.
It should not affect performance however may effect sperm count and reproductive capability.
Had, past tense. Either it came down on it's own or with help. Either way, you only need one to produce sperm and both may be working. There may be other issues, but by itself, one undecended testicle should not stop you from producing sperm.
Err... Assuming you have 2 testicles... 100% Divided by 2 = 50% So 50% in each testicle :)
Yep; half the sperm. Logical, right?
Yes ... although the amount of sperm may not be sufficient to fully fertilize the ovaries.
One testicle can still produce millions of sperm. Your sperm output is more likely to be affected by other things (tight or too warm clothing, diet, alcohol, drugs etc).
Although it is possible to father a child if only one testicle is removed, some surgeons recommend banking sperm as a precaution in case the other testicle should develop a tumor at a later date.