Welcome Kalkkis!
Weapon accuracy shows -10? when it should presumably show +10 for size.
The -10 you see listed out by the weapon when firing is not size-related, but appears because you have some system corruption, which can reduce your accuracy. This is also why it has a '?' beside it, because it may not actually take effect (only a chance, but it's there to remind you of that possibility). Any modifiers listed beside weapons in targeting mode are weapon-specific, so you won't see anything related to the target there.
Analysis info shows +0% to hit when it should be +5%.
Yep, that one's definitely a mistake on my part, thanks! Internally the output string assumed it was an integer, when the value is actually represented as a float, 0.05%, so it was rounded to 0 for display xD