In South America, how did Native Americans and Polynesians get along?

tl;dr-- there is no way currently to know most of the details you're curious about.

Polynesians settled some of the Pacific Islands- but they are just the most widely dispersed cultural group in the Pacific. The Austronesians, the linguistic and cultural ancestors of the Polynesians were already accomplished navigators before a branch of them could be said to have developed the proto-Polynesian cultural/language amongst the islands of Samoa-Tonga-Fji. So to answer your queries:

1; who knows what happened. Neither group spoke a related language. Exchanges certainly took place considering the presence of the coconut in South America and the Sweet Potato across much of the Eastern Pacific. We can imagine it must have been peaceful as the Polynesian words for sweet potato Kumala, Kumara, etc. are very close to words used in parts of South America Kumar, Kumal, etc.. That sort of linguistic exchange or transmission wouldn't necessarily happen without the two groups interacting in some meaningful way.

2; There is no way to judge the reaction.

3; I suppose I addressed this in 1, but it was probably peaceful. Polynesian voyagers didn't travel in groups big enough to have engaged in any sort of conflict.

4; No way to know. Certainly linguistic differences would have been paramount, and the absence of any genealogical or cultural connections would have made the people seem quite novel; but how they would have interpreted that information on either side of the beach is beyond our ability.

5; They both had unique technological tool sets. I'm not aware of any methodology to measure technological level in such a broad context. While questions like this can come naturally and appear interesting at first blush when you start thinking about how you can even scientifically measure something like technological level, the impossibility of doing so becomes clear. Each developed under very different circumstances.

6; probably not. Neither had endemic diseases to pass on that we know of.

7; There are some suspiciously Polynesian looking place names- especially some fishing areas along Northern South America and into Central America. There may have been even more at some point in the past before colonialism began reordering and renaming landscapes and places. There may be some chicken DNA and even some human DNA- but more of that remains speculative; Polynesians definitely went to South America during subsequent centuries when European colonialism spread across the Americas and Pacific- so some of those DNA introductions could date from that later period. Advances in genetic science may help illuminate this more in the future and strengthen claims of some residual genetic connection.

8; impact for who? For the South Americans- yes definitely European contact represented a seismic shift. For Polynesians? Well the sweet potato became a key crop- without it settlements in the far south, like Aotearoa (New Zealand), would likely not have persisted- and populations might not have reached such high levels. So for Oceania, or Polynesia specifically, it is incredibly important-- for the islands it opened to settlement, the populations that expanded, and the further proof of the skill of Polynesian navigators. Remember, just a generation ago, there were still loud voices that claimed Polynesian navigation was a myth and that islands were only settled by castaways. I would also add, that while European contact was also transformative in the Pacific- if you had asked that question 200 years ago the answer might have been the sweet potato was more impactful. Who knows what appraisals or new understandings will exist in 200 years.