Windows, trim, doors - https://www.thesimsresource.com/downloads/details/category/sims3/title/scania-build-set-part-1--windows-and-trimmings/id/962674/
https://www.thesimsresource.com/downloads/details/category/sims3-sets-objects-construction/title/scania-build-set-part-2--doors/id/970022/
Sauna - https://aroundthesims3.com/objects/room_downtown_39.shtml and https://aroundthesims3.com/objects/room_downtown_38.shtml
Rustic Log - https://www.thesimsresource.com/downloads/details/category/sims3-sets/title/rustic-logs/id/937915/
Wood Textures - https://www.thesimsresource.com/downloads/details/category/sims3-sets-patterns/title/wood-pattern-set06/id/1066501/
Bunnies - http://silverowlblog.tumblr.com/post/179223842291/ts4-to-ts3-leosims-rabbits-little-pre-simblreen
Guinea Pigs are already in game.
Apple tree is already in game but there are these, I'm sure you can find something to work. I think there are mushrooms at the bottom of the page - https://aroundthesims3.com/objects/function_decorative_plants_09.shtml
There is a cute basket with knitting in this set (my internet was not cooperating so couldn't get to the specific item) - https://www.thesimsresource.com/downloads/details/category/sims3-sets-objects-livingroom/title/jasmine-living/id/1250269/
Not sure what you mean about stairs, but here is objects for under stairs. https://www.thesimsresource.com/downloads/details/category/sims3-sets-objects-study/title/under-stairs-shelving/id/1090382/
There are a few others as well, dog house, dresser and bed that will fit under stairs. Google "under stairs objects".
You can use regular walls along stairs instead of railings.
Doubt there is a "hay pole" (had to look that up) but hay stacks and bales, both square and round are in the game already.
A mangle (had to look that one up as well). Doubt it. But there is this set that looks rustic - http://modthesims.info/d/418119/budget-bathroom.html and https://www.thesimsresource.com/downloads/details/category/sims3-sets-objects-kitchen/title/gypsy-kitchen/id/1108440/ - not sure what you want the mangle for.
There is this too but the animations are not quite right - https://www.thesimsresource.com/downloads/details/category/sims3-objects-furnishing-plumbing-sinks/title/victorian-charm-kitchen-dry-sink-tsraa/id/1026089/
The only berries I'm aware of come as part of a set - https://store.thesims3.com/productDetail.html?productId=OFB-SIM3:72092
or this - http://modthesims.info/d/516243
Juniper tree, already in game. See here - http://modthesims.info/t/427058
This could pass as a mood ring - https://www.thesimsresource.com/themes/goth/downloads/details/category/sims3-accessories-rings-middlefinger/title/sintiklia--ring-brilliants/id/1252143/
Pirttipöytä! - Looked this up too. Picnic Table from what I gathered. Google search "around the sims 3 picnic tables", look at images and click the one you like, or all! I found 4 of them. Picnic tables are outdoors only furniture. If you are looking for something for indoors???? You might have to mix and match something to make it look like one. The thing is...benches don't work with dining tables, sadly.
For all other objects - Google is your friend. Or http://sssvitlans.tumblr.com/sims3cc
Well, hope this helped you and I just wanted to say that I found a really cute Scandinavian world just yesterday, so this 'ask' is ironic, in a way. It's here - https://gemeinsamesims3nachbarschaften.wordpress.com/adventskalender-2014-2/adventskalender-2014/
Good Luck, Create a World Tool, Beta is a pain.
Regards, KFL