A number of prominent HNers would be all to happy if you copied their ideas, business models, or execution techniques. Many of them have blogs that are essentially, how to launch a business just like this in N easy steps. Some of them will even answer questions and coach you if you ask nicely.

That said, it is probably polite to not outright copy. For example no one likes the sites that mimic Stack Exchange's layout and even copy their content. Similarly if you copy someone's idea, market, and business model wholesale (without asking), perhaps expect some flak.