I suggest that you wear chain leggings as opposed to plate greaves.
Extensive testing has shown that plate armor does nothing at all against metal bolts/arrows in the current version of dwarf fortress, while chain mail provides modest protection. Multiple layers of chain mail do not improve protection, so the best possible protection would be to wear chain mail shirt and leggings, breastplate, helm, gauntlets and high boots.
Given that all armor performs extremely poorly against projectiles, I definitely would recommend investing in/training shield and dodge skills. Also, being immune to pain is a huge benefit, as arrows chip bones extremely often.
You might even consider not using plate armor at all, as it's very heavy, but probably your adventurer will be strong enough that he won't be slowed down too much by the weight. Also, it definitely does help in melee combat.
Technically, if you want the best possible protection for a vanilla adventurer, you should just wield 10 or so shields. Use the lightest material possible, as all shields block equally well. This is a filthy exploit of course, but doesn't actually involve modding...
If you want to mod bows to behave somewhat less like railguns, you could consider reducing [SHOOT_FORCE] for bows and crossbows (in /raw/objects/item_weapon.txt) to something between 25 and 50. There is some discussion of this on page 9 of the testing thread mentioned above, as well as in
this thread. Bottom line, even reducing [SHOOT_FORCE] to 25 has almost no impact on bolt effectiveness against targets which are naked or have armor inferior to the bolt material, but does cause bolts to deflect off of targets with iron/steel armor relatively often. While modding of course is not vanilla, I think there is a clear argument that bows are currently overpowered to the point of being broken. Also, we do not yet fully understand how deflection works, so I can't say what modding is required to get a "realistic" behavior for bows, or if this is even possible through just modding the raws.
edit: I haven't found it possible to survive long in vanilla adventure mode without either exploiting shields or sneaking everywhere, but maybe I'm just not very good at it...