I'll try to answer some of the questions mentioned above. My background is in tankers and these really big engines are used in container ships, so I don't have specific numbers nor do I have my design manuals close at hand.
Oil Changes - Oil changes are rare, though becoming more frequent as technology improves. These engines burn oil at a predictable rate - it's contracted when you buy one. (The newer engines burn less oil.) As a result they are regularly topped up and the oil is designed so that these top-ups are sufficient to replenish the additive package. The oil is also heavily filtered, centrifuged and dried. It is also sampled, usually monthly, to check for impurities (metal, water, etc.) so that problems can be detected and repaired. Finally there are often up to three separate oil systems, each running a different oil. The crankcase charge, which cools the bearings and other sliding parts. Cylinder oil is injected directly onto the liner walls to lubricate the piston and rings - most of this is burned. Finally some ships have a dedicated cam shaft lube supply as the cams are highly stressed and it pays to keep the oil extremely clean and often heavily supplemented (Royal Purple Synerlec works great!).
In the old days ships were built around the engine rooms as steam plants took a while to build. Now the engines are factory built and dropped into the engine room before the deck goes on. Conveniently the engine factories are usually colocated with the large Asian shipyards that build the big box boats.
