I'll update people's location names soon.
Okay, questions have been asked both here and privately. They will be answered here, but private questions will be edited for brevity and be anonymous.
I want to do [REDACTED] but I don't want anyone finding out
Almost everything is publicly accessible, because manipulating this much information privately will be a pain in the ass and make it impossible for any observers. The only things that are private are spy ring actions and results, mid-research tech and, optionally, turn submissions.
The island at C4 F11 and K5 are there any defensive terrain bonuses there?
There's nothing special about C4, F11, K5 or any other island that is within the same subregion as the mainland.
The larger islands of C2-D3 and E2-F3 are separate however, and will require boats to access.
What time period are we tech-wise?
Currently early medieval. Shortswords and longswords as two different breeds have not developed yet, there is only the sword. Cutting edge armour is alternate solid and rivetted maille.
Can docks be built and if so how much do they cost as well as wharf and do docks receive outside trade or only trade between players?
They can be built with tech.
Will the empire receive outside invasions or grow their army?
Spoilers.
If I am not mistaken, materials inccome is calculated monthly, while food income is yearly ( harvest). Does that mean that as long as I build mills the month before harvest I get the full bonus? Or is food income also calculated monthly?
]Correct, material tax is acquired monthly and food is yearly at the harvest. And correct, as long as a mill is present before the harvest you gain the benefit, because I can't be bothered making it more complicated than it needs to be.
Also, I see that most buildings require generic materials and quarries produce 2.5X times as much than lumber camps. Before I spam quarries for early income, is that intended?
Regarding quarries vs lumber camps, yes it is intended. Stone however, is only useful for construction and you need a lot of it for stone-only constructions. Logs are also used for weaponry.
You can indeed build multiple quarries/lumber camps at a single location. As one quarry produces enough stone per month to build two more quarries a compound investment can quickly create a lot of income.