A given when one understands that full time standing armies didn't exist for the majority of the period CK covers either. You had very little control of what your regiments were composed of in CK, though there was of course different types of soldiers. If navies became similar to the original CK recruitment system, I might be interested then. I just don't want to see a massive amount of ships being built by coastal counties and Kingdoms, and then see naval battles routinely where hundreds of ships clash against one another. It's bad enough you sometimes have battles that were far more epic than they actually would've been.The main problem here is that almost no full-time, professional navies existed.
I notice most don't list the amount of ships present, and most are also either Italian, Byzantine or Arab. Again, seeing naval combat wouldn't be a bad thing at all and prove useful, but by no means should it be as common for most Europeans as it is in EU3 .There are literally dozens of examples of naval conflicts during the Middle Ages, but they're simply not well known. For example, Edward IV of England conducted a full-scale naval war against the Hanseatic league which involved numerous large fleets fighting in the North Sea.
You can look here for a rough list of conflicts, though it's fairly slapdash as lists go.
I do propose though a solution to solve perhaps naval overcrowding if they add it. Place an actual hard limit you can't go past dependent on wealth of a province and perhaps prestige of the liege. For the most part, only Kings will have fleets, though very wealthy Dukes should have the ability (examples being William the Conquerer's half brothers and their donations to his overall invasion fleet) to build a fleet themselves. In my oh so humble opinion, counts should never build a fleet.