I already have one person on a waiting list, and a few others who have asked if there's room, but y'all have first dibs.
Mmm. I'm not sure if I can do that. There has to be some trade off to multiclassing, even if I'm purposefully being more lenient with it. Giving the second attack based on character level would be like giving a multiclassed wizard access to 3rd level spells at level 5, even though they took two levels of Cleric. Sure, the spell slots stack, as they're both casters, but higher level spells are still tied to class level. It works the same with multi attack, in my opinion.
1. Mariner's fine.
2. Fists of Unbroken Air make your attacks ranged attacks, but it's not a ranged weapon. So archery wouldn't affect it.
3. Same as 2. Sharpshooter works with ranged weapons, not just ranged attacks. At least, that is how I'm going to rule this.
Adding the Ranger levels makes sense with his backstory. Just keep in mind that mechanically, you'd be trading a d6 martial arts die, second attack, slow fall (not really needed), stunning strike, as well as quicker access to higher level Monk abilities for favored enemy, favored terrain, a fighting style and two spells. You don't really need the armor or weapon proficiencies as a monk. Whether that is a good trade off is entirely up to you. As if fits the backstory, I don't mind if it's less than optimal. Just making sure you see the comparison between the two clearly.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.