A proto-Angmar in the Second Age
 

If Sauron sent the WK and another Nazgul to raise a pre-third age Angmar during the reigns of Elendil in Arnor, how would a war between Elendil and the WK be?

Since Arnor was at the peak of its power in the Second Age, I doubt any such small realm such as Angmar could have stood much chance.

The number of troops required by Sauron to have been sent north for a serious assault would certainly have been noticed by his enemies, and would have left Mordor itself open to attack.

I rather think that Sauron was desperately trying to regroup after his surprise dis-embodiment in Numenor, and scraping up enough troops just to deal with Gondor. And the notion of offensive ops against Elendil and pre-Last Alliance Gil-Galad/Lindon strikes me as Sauron sticking his head in a hornet's nest. One Nazgul? Curbstomp (let's not forget that the W-K was afraid of one Noldo, Glorfindel. You think he can take an army of them?)

The 3rd Age Angmar project took centuries to pay dividends- against a weak and divided Arnor.

Yes. While referring to Lindon, not Arnor, Appendix A is entirely explicit on this point:
It's emblematic of how doubtful Sauron's means were at the end of the Second Age that his enemies were able to invade his territory, rather than the reverse. Some short-lived early victories against newly-founded Gondor notwithstanding, Sauron was weak* at the end of the Second Age, and his enemies were strong. That's why he spent the next three thousand years wearing his enemies down through subterfuge, unconventional weaponry and proxy wars.
*And this is taking into account the remark in Myths Transformed about Morgoth's First Age power compared to Sauron's in the Second.

It's also the case that Tolkien said (can't find the source at the moment) that a significant factor in Arnor's later weakness was that it was stunted in childhood, by the massacre of most of its fighting men at the Gladden Fields.