Scripture

No, it's not impossible to understand. No, KJV is not better and did not come first. Just dive into the Douay-Rheims and don't look back. One pro-tip: reading old Catholic books can help you get used to the "archaic" language because these books often quote from the DRV.

Masses always have one Epistle or Lesson (at least) and one Gospel reading. On top of that, the Propers usually come from Scripture, too. One caveat: the readings for some weekdays are simply repeats of Sunday. Just be aware of that if you base your reading plan off of this.

This page has great examples for different levels of readers, all with the end of reading the whole Bible in a year. Unfortunately, the Advanced plan based on Matins is only available for those with Scribd subscriptions.

The Catena Bible app, built by Orthodox Christians, has a lot of great options for reading the DRV with the Catena Aurea and an assortment of other commentaries. If you create an account with the mobile app, you can also curate your own Bible reading plan (Bible in a year, Gospels in four months, NT or OT in six months, etc.).

Although the footnotes by Challoner in the DRV are nothing to shake a tail feather at, sometimes some added expertise is in order. A popular collection, though it only covers the Gospels, is the Catena Aurea compiled by St. Thomas Aquinas. Another revered commentary, though not completely translated into English, is that of Cornelius à Lapide. But for most serious readers, the go-to is Haydock.