On the borrowing, the chances of the Norse lending to native Americans is close to zero. They were xenophobic to the point of killing some to find out what colour blood they had. As for the conception of credit you need a more sophisticated conception of market economics than barter with people who can say "Thank you very much" then disappear into the hinterland and never repay.Yes, but the hunter-gatherers can buffer against demand fluctuation either by borrowing from the farmers in bad years, or storing up stockpiles of low volume high value durable goods in good years (like furs to sell to farmers or silver received from farmers).#
Short of farmer produce (cheese, domestic animal meat). If it does not happen to be a simultaneous lean year for hunter-gatherers, then the hunter-gatherers can get high prices for their produce like wild animal meat or fish dried or smoked.
As for buying food from hunter gatherers, yes the later Europeans did that in bad times until they had sufficient numbers that they could run the natives out. I would expect the Norse to do the same only much quicker.
Yes, the large amount of firewood would help. However, the increase in production could easily be absorbed by Norse consumption. There is evidence that Greenlanders were so iron poor that they were forced to squeeze out every last ounce from what they did have. Increase the amount of iron available to them and they and the Vinlanders could start to use it more prolifically.Yes, but that was done at a number of spots. The settlers of Iceland tried it locally, too, but soon ran short of firewood, like Greenland.
Vinland, with good local firewood supply, will smelt iron, and not only for local consumption but to sell to the bigger markets of Greenland and Iceland and yet bigger markets of North America.
I admit I had forgotten about the hides trade, but it was still a case of quality goods in small numbers. You are looking at two boat loads in a good year and none in a bad one.The OTL exports of 13th century Greenland were listed as walrus ivory, seals - as well as rope, sheep and cattle hides. Europe had a plenty of these locally - yet they covered the cost of transport to Europe.
The Greenland Norse kept sailing from their settlements to north, areas of Disko Island and as far as Upernavik Runestone. Only for hunting (no Eskimos to trade with yet).
This assumes that the Norse have sufficient spare iron for serious trade, especially as the Greenlanders will compete for it. On purchases, sea shells have a limited market whilst copper will require tin or zinc to have much utility. In addition you must swap it at a ratio where you in effect end up with more metal goods than you would if you retained the iron traded. If you don't then why trade to lose?Vinland Norse can quite reasonably afford trade trips to Hochelaga and to New England. There was, OTL, a trade network of Mississippi Culture, and trade goods reached Mississippi Valley from Atlantic coast (seashells) and Lake Superior (native copper). Something was paid in return. The iron tools sold by Norse at Hochelaga would feed into Mississippi Culture trade network.
There is still the shipping issue in the long turn round time between North America and Europe and without that Vinland's trade will remain marginal. Greenland and Iceland are just too poor to compensate. Building more ships won't help this. To make it non-marginal you need the sort of profits that the later Europeans made on the spice trade. There is nothing in the region that will give you that.