1) The Norse were the sort of people who killed strangers just to see what colour their blood was. Assume eventual bad relationships with any natives.
2) If the Norse in Labrador had excess fish and seals (and I assume that you are talking about them) they are more likely to trade such stuff with Greenland in return for more iron along with European imports. If you are talking more generally more fish means less seal in the diet.
3) The Norse may not in theory need the deep forests, However, if they cut them down they can create pasture for cattle, sheep and goats and they can trade the timber with Greenland for the stuff in 2 along with animals to graze the pasture. Greenland was timber poor and milk products are part of the ideal Norse cuisine.
A successful Norse Markland is not good for any natives.
1. That's a stereotype. Plenty of strangers (i.e. people from Iceland, Norway, and Denmark) set foot in medieval Greenland and traded with the locals, sometimes to the obvious disadvantage of the locals, and didn't catch an axe to the head. The Norse were perfectly capable of engaging in long-term trading relations (i.e. with the Sami or the people of Bjarmaland) that did not result in the sort of total war seen in Greenland or the Indian wars of 17th century colonial America.
2. I'd think it the other way around. Greenland has few trade goods beside luxury goods (before the 15th century when the codfish industry could easily have been expanded there), but does have high demand for quality timber and iron. So I think Markland would export iron and timber to Greenland and import excess European goods or maybe quality livestock (probably animals rare in Greenland like horses and pigs). Trade with the natives makes more sense. It replicates the interactions individual bands of Innu and Naskapi had with each other (interior bands would trade reindeer skins and meat for fish and seals), is mutually beneficial, and gives easy access to a good with some value (as leather, although that's not really valuable as export).
I suspect the natives could also be used to obtain walrus ivory (walrus would have not been common south of the Arctic circle in Labrador), polar bear pelts, and gyrfalcon feathers (also valuable trade goods Greenland sent back to Norway) which would further reduce Norse-Indian conflicts because the Norse would not be hunting in their territory. This also means less dangerous sea voyages for the men of the colonies, so they could focus on managing their farms, building ships, and crafting goods to sell to the Indians.
3. That would not occur for decades or more. Greenland is a small market (no more than 3,000 people), and there might be political issues with selling timber in Iceland (since it competes with Norwegian merchants). By the time the Norse would need to truly expand their territory, they would have the population base necessary to win an Indian war. Potentially they'd always be militarised than the Greenlanders because they have more iron and the Indians are always a presence unlike in Greenland where the Inuit were invaders--Greenland was a peaceful land where most violence was either fights between individuals or dealing with dangerous polar bears.
Also compare the area of the unglaciated areas of southern Greenland to Labrador. Just a fraction of coastal fjordland in Labrador offers more land to the Norse than Greenland, and in many cases higher quality land due to the existance of sheltered areas where groves of trees grow.
I'd say we can't really know how Norse-Beothuk relations would have evolved over time. But it is definitely a mistake to assume that it was a template for how things would have gone elsewhere, and most certainly Norse-Inuit relations are not a template given they occurred in a very unique context which is impossible to replicate elsewhere.
Then consider that on the journey to America, they basically island-hopped. Iceland sucks. Greenland sucks even more. Helluland sucks most. Markland, if we assume it's Labrador, sucks less than Iceland, but is full of angry strangers. Finally you get to Vinland which might be Newfoundland or more south and discover that it's also pretty meh, and also full of angry strangers.
That's a lot of coast to cover, and in order to establish a colony, you'd have to establish them in all those places mentioned above that are barely worth considering. And don't forget, no swanky navigational tools the Portuguese first used centuries later. It would simply be comically expensive and a logistical nightmare. Nobody would agree to this.
Iceland doesn't suck by Norse standards. It's got a bunch of great land to raise cattle and sheep, used to have a decent amount of forest, and is far from any powerful king. The typical medieval Norseman mostly just wanted a big farm, a good wife, a lot of children, and to be left alone by wars and oppressive rulers. Even Greenland isn't so bad, since in some valleys it was possible to grow barley in some years during the 11th and 12th centuries. We should assume the same for most of Labrador south of the Arctic circle, and certainly for the southernmost parts which are akin to Iceland.
And the Norse also had very good navigational tools. They used sun compasses that could determine the direction of the sun on all but the most overcast days (or nights), which is helpful since at high latitudes the nights are very short in the summer. They could roughly determine latitude and compare it to the latitude of known ports.