Yes, you can breed a leghorn with a RIR. Their eggs lighten up to a cream color instead of the darker brown the RIR normally lays. Anytime you cross 2 great layers, the sex-link it produces is always better than the true breed. I hope this helped answer your Q...good luck!
That's not true. They are highly productive, and breed very well.
There is no definite answer, since there are two options for practice - successful and not. I bought chickens from Amber Waves. They have Lifetime Support at all stages. Only they can tell you what to do in your case. But the question is difficult enough. Since there are successful experiments in crossing different breeds, as well as failed ones.
Yes you can but it might take a few tries because it is really rare the are furtile