This is a really neat spot, and I highly recommend it. Major recommendation: Bring plenty of battery powered lights if you want to be able to do anything at night. Like the other reviews say, there is limited lighting, so it got really dark. We brought a nice string of lights and a couple of flashlights (and a few small lights are provided), but it was still a little too dark to do some of our planned activities at night.
-It is indeed cold, so bundle up. However, the heated blankets on the bed are perfect, so we weren't cold while sleeping.
-The bath outside is nice (cool blue lighting at night), and it's got a shower nozzle to rinse yourself off. You have to walk about 50 feet away from the treehouse to access the bath, and it is about 10-15 feet from another little cabin, so don't necessarily expect a totally private feel. There are 3 walls providing cover, but the bath does look out into the forest on the fourth side. There was no one in the other cabin when we stayed, so it was a wonderful, private bathing experience. We loved it.
The bathroom inside the treehouse is downstairs, and it's just a toilet and sink behind some large hanging bamboo shoots. It is not enclosed, so don't expect to be able to do your business in a private space. It was nice and clean, though.
-Wifi: Don't expect to be able to use the internet, but there actually was some reception there. My partner and I did still receive some messages, but we couldn't send any.
-The cabin is a ways away from the hosts' cabin (at least 50-70 feet, or so), so my partner and I did feel pretty separated from society. It's a pretty area, lots of redwoods in the surrounding area, and it's very quiet at night with lots of stars above. Check it out for yourself!