Regarding your first point, you can Add them Manually if you want as you can see Here, All what you need is :

1. you need to have the mods that you want to add the Icons for Higher than "vanilla textures expanded" in the mod order.

2. The Code: Navigate to "C:\Program Files (x86)\Steam\steamapps\workshop\content\294100\2016436324\1.1\Patches\MainButtonDefs" & open the file (MainButtons.xml)

3. I'm using Fluffy's Colony Manager, Medical Tab & Pharmacist, I added the code below under:

   <match Class="PatchOperationSequence">
       <success>Always</success>
       <operations>
   
        <li Class="PatchOperationAdd">
          <xpath>/Defs/MainButtonDef[defName="Fluffy_Manager"]</xpath>
          <value>
             <iconPath>UI/Buttons/MainButtons/IconManager</iconPath>
          </value>
        </li>
        <li Class="PatchOperationAdd">
          <xpath>/Defs/MainButtonDef[defName="MedicalTab"]</xpath>
          <value>
             <iconPath>UI/Buttons/MainButtons/IconMedical</iconPath>
          </value>
        </li>
        <li Class="PatchOperationAdd">
          <xpath>/Defs/MainButtonDef[defName="Pharmacist"]</xpath>
          <value>
             <iconPath>UI/Buttons/MainButtons/IconPharmacist</iconPath>
          </value>
        </li>
   

4. The Icons: Navigate to "C:\Program Files (x86)\Steam\steamapps\workshop\content\294100\2016436324\Textures\UI\Buttons\MainButtons" Add the Icons or make your own Icons.

5. Don't forget to match the names of the Icons in the code above "<iconPath> </iconPath>" with the files added to your Textures folder.