Running Multiple Apps in the Same Browser
You should not run more than once SmartApp in the same browser. When SmartTiles and IDE are run in the same browser, they compete for a SmartThings session and keep logging each other out.
To add weather tile, go to IDE > My Devices > New Device, add SmartWeather Tile. It will be listed as one of your devices and you could pick it when you configure preferences of SmartTiles.
Adjust Tile Size
If you think your tiles are too small/big you can try to change app preferences. If you don’t achieve a desired result, add “&t=120” at the end of your dashboard’s URL and play with the value to see what works best for you. If you are using a desktop browser you can also use zoom in/out.
Grouping Switches and Dimmers
There were feature requests for one switch to control a group of switches. This can be achieved with Big Switch app by ST. You can find it on your mobile app. Tap (+) > More > Convenience > Scroll to the bottom and find “The Big Switch” app. Then set up the master and slave switches.
Also, check out this forum thread on Virtual Dimmer and Dim With Me.
To create a virtual switches or momentary push buttons, go to IDE > My Devices > New Device. Enter required fields and choose “On/Off Button Tile” or “Momentary Button Tile” in the type selection box. Then you can use it as any other switch and put it on the dashboard.
Since the app is designed to scale across a range of screen sizes, you get to define only linear order, the tiles will wrap to the next line depending on available space. If you want certain tile to appear on certain row/column for a particular screen size, just count the position considering sizes of other tiles.
If you want to change the style, I added a block of code for your custom CSS overrides. See this page for more detail.
Please note that SmartThings is currently experiencing an issue where some SmartApp preferences are temporarily lost. This may manifest itself as tiles order changing arbitrary. There is no workaround at the moment but the tiles may revert to the desired order once servers synchronize.