I just wanted to know if it requires things like new tables, columns, defines, AI strategies etc. in the database, or altered UI, to work properly.
Can you just take the .dll file from either the VMC or CP mods and add it directly into your own mod? No.
Both DLL's require a number of database table additions/alterations to work - at the very least you need to take the XML that creates/populates the configuration database tables - see CustomModTables.xml and CustomModOptions.xml - but also some others that push previously hard-coded values into the Defines table
As bane_ said, your first port of call should be the CustomModOptions.xml file
As of v75 of DLL-VMC ...
To make use of the hard-coded configuration pushed into the Defines table you will need to include the AiInXml.sql and GameInXml.xml files
You should probably keep AllText_en_US.xml, although the worst that'll happen if you don't is that you'll get broken text strings in the UI
Regardless of whether or not you are using the new Yields, you MUST include the four unified yields related files - UnifiedYields.sql, UnifiedYields.xml, UnifiedYieldsTourism.xml and UnifiedYieldsGoldenAge.xml - these four files are commented at the top "DO NOT DELETE THIS FILE!!!"
If you want to use the new yields (Tourism and GA points) as tile yields, you'll need to take the modded YieldIconManager.lua/xml files and the two associated .dds files, to make them appear on the map.
To make use of the API extensions, you must include the Extensions.sql file
If you want the STFU code, you'll need both the Stfu.xml and Stuf.sql files and additionally the InGameUIAddin file Stfu.lua
All other xml/sql files are optional. If you don't include any/all of them, the config code will detect the missing file(s) for the associated option(s) and switch the option(s) off - even if you try to switch them on. So if you omit the PassableForts.sql file from your mod, it doesn't matter how hard you try to enable the GLOBAL_PASSABLE_FORTS option, it will not turn on. (Well ... as with all things software related, you could hack the code to get around it, but then you get everything you deserve when the game crashes as it tries to access a database table/column that doesn't exist!)
YMMV with the CP dll
HTH
W