It is hard to describe the utter freedom I feel from being able to get on my bike and safely go... Anywhere. Even with my kids as passengers. It feels like I've escaped prison. Too bad I had to move to the Netherlands for it. But it's wonderful.
You can, of course, ask someone to leave your land if you need to use it. There's a reason that adverse possession takes years to decades.
Here is a Finnish web site on the topic: https://www.visitfinland.com/en/articles/finnish-everyman-ri... . Here is another: https://www.nationalparks.fi/everymansright .
> "What's the line between a tent and a cabin?"
You can pitch a tent. Not build a cabin, nor park a camper. Only temporarily. It looks like motorized transport on land isn't included (I wonder if e-bikes are allowed.) Though you can drive a motor vehicle on frozen lakes, rivers, and the sea, so perhaps you can take your camper out then and do some ice fishing?
> "How much are you allowed to modify the environment to make it suitable for camping?"
Not much: "It’s NOT allowed to… cut down or damage trees … collect moss, lichen, or fallen trees from other people's property … light open campfires without permission, except in an emergency". "In short, leave nothing but footprints behind."
> "How long are you allowed to stay before moving on?"
I can't find it for Finland. For Norway, "Tourists are allowed to stay in one spot for up to two days."
> "Are you required to remove your waste?"
It's forbidden to litter. I can't find what to do with poop - probably the usual burial is okay, depending on where you are. I would expect more notice about needing to carry it all out if that were required.
> " How close can you be to an established dwelling?"
A "reasonable distance from homes." Not "very near homes and other private buildings or through farm fields and nursery plantations which could easily be damaged".
It looks like "200-300 feet" is reasonable, from one site.