Build wise you dont want to invest anything in "secondary" DPS as you want to all-in on your main DPS. You can invest 100% in Bows and not be wasting any opportunity costs. Though bows right now are really bad, so even at 100% investment they wont be that great compared to...well, pretty much anything viable...
There are plenty of ranged bow builds you can find and use as a guide, but I'll just caution you to avoid the temptation to try and flex it to "get more" out of your TWF. Odds are you'll want to stay in archery even in melee range just because its better than your TWF. But if you do want to swap to TWF, you'll want something with Keen, since you wont be taking Imp Crit Slash or Pierce. Oathblade is a powerful and easily acquired option at L20 that will work just fine, and there are lots and lots of others you could grind for if you wanted more:
https://ddowiki.com/page/Category:Keen_items and
https://ddowiki.com/page/Category:Impact_items