How do I hang antique wall shelves?

Heavy masonry fixings offer the safest route. You want long screws that reach deep into the brickwork, bypassing the modern plaster layer entirely. Never rely on standard picture hooks. Most antique wall shelves are quite heavy even before you add books to them.

I have a three-tier oak set but the bottom shelf seems much deeper than the top one, is this a normal design?

Graduated depths are standard for this category. Cabinetmakers designed them this way to keep the centre of gravity close to the wall. It stops the unit feeling top-heavy and reduces the strain on the upper brass hanging plates. The practical benefit is clear when you load them. You place larger folios or heavy jugs on the bottom tier. The shallower upper levels take smaller paperbacks or delicate teacups.

What are the small drawers for?

Base drawers provided hidden storage in busy household rooms. They held small everyday items that would otherwise clutter the flat wooden surfaces above. In kitchens, they kept loose receipts or string out of the way. Library versions saw different use. Owners stored reading glasses, paper knives, and small desk accessories out of sight.

There are two brass rings on the back of my shelves but no wire between them, should I add a wire to hang it?

Adding a wire is a risky idea. Those brass loops are called mirror plates and they are designed to take a screw directly into the wall. Hanging a rigid wooden frame on a slack wire forces it to lean forward into the room. A wire also pulls inward on the side uprights. The joints on most antique wall shelves were built to bear a downward load, not a sideways compression. Direct wall screws keep the whole structure flat and stable.