I am probably just not finding where this info is located, but there are several new features that I can not find the details on how to implement:
Yeah there is no thread about these infos yet. It was described in the german section (since someone asked the same question), not sure if there was an english description somewhere as well 
•[New] Custom journal ("server notes") now also supports images What is the syntax in the journal.xml file?
Just put the image (jpg, png or gif) into the server directory and put a new <image> key into your journal.xml file, e.g.:
<image name="myImage.png" width="256" height="256" page="left" posx="0.5" posy="0.75" pivot="center"/>
•[New] Multiplayer servers can now put their logo on the loading screen (server_custom_logo) Syntax? File type/size restrictions? I assume in the server.properties?
Basically also just put the image (jpg, png or gif) into the server directory and put the image name next to server_custom_logo key in the server.properties file. Basically there is no size restriction, but it's highly recommendable to keep the image as small as possible (since the client has to download it when he connects to the server). Personally I'd recommend to not exceed 512x512 px 
•[New] Weather preset (sunny, default, unsettled) can be selected in the game settings (Singleplayer only), MP setting also available Syntax? server.properties?
In the server.properties file it's the settings_weather_preset key. You can use "default" for default weather, "sunny" for good/sunny weather preset and "unsettled" for bad/unsettled weather preset.
•[Change] Increased visible distance of images (depending on their size), can be adjusted in config file config.properties? Syntax/values?
This is only a clientside setting. You can change the game_customimage_visible_distance key in the config.properties file to adjust the visible distance. E.g. "1.0" is the default setting, "0.5" reduces the visible distance by half, "10.0" provides a ten times bigger visible distance etc. 