Glad to be of assistance where I can.
To be able to clear out your underground camp slots means that you need the necessary amount of materials required in your inventory.
This wiki page has a table showing how much materials is needed to clear out each camp slot.
Just as you have already started to clear out your 4 height slots....you just keep going until eventually all slots are cleared out in all rows of your camp.
You will see that there is 2 rows of each height (2,3 & 4) slots in your camp.
You can gain more of the materials (lumber, stone, iron ore, tin, coal & copper) required to clear out camp slots by doing the repeatable mines in the "Material Map"....as you progress through the game more locations will become unlocked in there.
You make iron & bronze in your "Foundry". To make iron you need iron ore, lumber & coal. To make bronze you need copper, tin & coal.
The Professor Switch System is designed as follows:
- Daytime setting is used to make your camp to be higher in regeneration which is the setting you use for when you are actively playing.
- Nighttime setting is used to make your camp to be higher in capacity which is the setting you use for when you are going to be away such as when you are sleeping/working.
- You can tweak & change the camp equipment in your 2 camp settings at any time depending on what you need.
There are different types of carts available in each region.
Carts are a piece of capacity camp equipment that are usually some of the highest capacity available in each region.
It's a good idea to try to stockpile green gems & precious stones/jewels as they are very useful "currency" to be able to buy stories, camp equipment & other useful items.
I personally would never spend green gems to buy food/energy items.
I play via Android mobile phone app so pillars, windmills & decorations are not available to me unfortunately....however there are a lot of helpful threads in this forum about these types of items.
Other investments worth considering in time is the Golem, Energy Saver, Experience Booster & Last Tile Finder.
Green rings are another very useful item...in particular they are very useful during Double Materials week as they are used in the repeatable mine "Chambers Of Fortune".
There are some older stories that are currently available for 100 gems that you can also obtain green rings from.
In relation to the E-Book I didn't even know that it existed so unfortunately I cannot give you any opinion or advice in relation to it.
But perhaps some of the other moderators or players such as @gamemaster, @BlameTheParrot, @ROMI, @Abhi, @Roeland, @red_herring, @Chani (sorry if I missed anyone) might be able to provide more information in relation to this among other things (such as pillars, windmills, decorations, Facebook, portal & other Web GL items).
Hopefully this information is of some assistance to you.