There will be options for heavy hulls, which will add armor for a small cost in speed. I’m probably also going to add a mortise-and-tenon hull type, which will add armor at the cost of being more expensive to build and repair. I’ve already added rules for clinker hulls (the default is framed carvel just because that’s what most people are familiar with), so adding a mortise-and-tenon carvel would make sense also.
Oarsmen are somewhat abstracted - oars weigh 1 stone per 2 rowers, but the rules don’t say whether that’s 2 oars each weighing half a stone, or a 1 stone oar with 2 rowers on it. If one really wants to get into the details, the formula for rowers [(Useful Length/3)*((Beam-8)/2)] is based on the math of how many rowers can be crammed into a space. The Useful Length/3 gives the number of files of rowers; each file needed around 3 feet of space to operate efficiently. The ((Beam-8)/2) is a rough estimate of how many rowers can fit next to each other in each file. A ship generally needed 2 feet of space from the hull to the first rower for leverage, plus a 4 foot walkway down the middle for people to move about on the deck, and each rower took up 2 feet of space. So, a 12 foot wide ship can have (12-8)/2 = 2 rowers per file; it’s only got 1 man per oar. A 16 foot wide ship can have 4 rowers per file, or 2 men per oar, and so on. Or, working the other way, each time you add an oarsman to an oar, it adds 4 feet of beam to the ship (one man per side times two feet per man).
This particular merchant ship, with 106 rowers, has 26 files of 4 and a file of 2 (probably at the bow, where it starts to narrow but can still fit shorter benches). The “50 oars” would likely be 24 two-man oars and a pair of one-man oars.
tl;dr answer: it’s abstracted into the rules.
The ability to add extra men per oar is also part of why ships are limited to three decks; it’s pretty much physically impossible to superimpose four decks’ worth of oars and actually get a useful working stroke out of them, and moving forward to the Age of Sail, ships generally carried cannon on three decks or less (and there are rules for forecastles and sterncastles for the partial fourth decks that were rarely used).