Responding to your first question (I'll let Breezy handle the other two), to stagger the unlocks a bit, we went for shortbows at X0 Fletching level, crossbows at X3 Fletching level, and shieldbows at X5 Fletching level.
The eternal/primal equipment releasing with 110 Woodcutting & Fletching 9th December have similarly staggered unlocks, so that you have some more gradual unlocks on your journey from 100 to 110. We'll see what players think of that and I can apply that feedback to the re-tiering.
Here's how the weapons are currently arranged at the lower tiers: