It might be worth considering at any latitude; despite the association with sunlight, the NIH notes that "perhaps surprisingly, geographic latitude does not consistently predict average serum 25(OH)D levels in a population". (http://ods.od.nih.gov/factsheets/vitamind)

Get your levels measured and dose accordingly. Most people are deficient in a number of areas, and you can get screened for them all at once.

In the absence of that, if you're just making a qualified guess, you should probably dose significantly more than 1,000-2,000 IUs/day. The daily intake required for toxicity to be an issue are very high (sustained total intake of around 20,000 IUs/day). It's also generally recommended that D3 supplements are taken alongside a K2 supplement.

"Most people are deficient in a number of areas, and you can get screened for them all at once."

May I double-click on that? What do you mean? Who do you go to, and what exactly do you say to them? Which areas are you referring to?

Talk to your doctor. They can take a blood test and send it off to analysis. It can be somewhat expensive. When I said "all at once" I didn't mean that a simple biochemical test can reveal all deficiencies, obviously, but that a single blood test can be sent off to have many different tests done. I'm not yet sure exactly how it works in the US, sorry.

The kind of deficiencies I had in mind would be vitamin (e.g. D, K), mineral (e.g. iron, calcium) and electolytic (e.g. magnesium, potassium).