P-MAN, you are just beginning to find out how good EB really is. The depth of this mod is great with each faction able to do different things and geography affecting building and recruiting strategies as well as the warfighting strategies. You have two specific questions relating to the building of ships and how MICs affect recruiting.
Firstly you need to be aware that trading ports are different from naval ports (the ones you need to build warships). You need a trading port before you can build a naval port, but you cannot build naval ports everywhere, they are only possible in some regions. I have not played the Casse so I cannot tell you in which regions in the British Isles you can build naval ports I am afraid, but do make sure you have not just built trading ports. You should study your Builing Tree:
https://www.europabarbarorum.com/web...Casse_v0.2.pdf
As for recruiting and MICs it is quite common for some levels of MIC to add no new troop types to what is recruitable.
You should study the Recruitment Viewer available at:
https://www.europabarbarorum.com/downloads_misc.html Its not 100% accurate but its as good as it gets. It will show you the geographical availability of a unit type, whether you need native or regional MICs to recruit and what level of MIC you need as well. Tie this in with your Building Tree and you can work out what type of government to build to allow for the most useful combination of MICs.
While I am at it I find the following site excellent for reviewing the strengths and weaknesses of each unit type:
http://europabarbarorum.heimstatt.net/