Lameller Armour

I can't think of any historical examples of lamellar bracers/vambraces. Lamellar body armour is typically sleeveless or has pauldrons that cover just the shoulder or come down to the elbow. Forearm armour is typically separate from the body armour, and I know of none that is lamellar. Japanese forearms are usually part of sleeves covering the upper arm, forearm, and back of hand, and can be mail, mail-and-plate, splints along the forearm, large plates tied to the sleeve, or hinged plates enclosing the forearm. Plate vambraces (i.e., bazubands) were common with lamellar in West and Central Asia. Some Sassanid art appears to show mail forearms (and legs) with lamellar (which comes down to the elbows).

You should be able to make working bracers with lamellar plates, but I don't think there's any benefit from lamellar contruction for bracers. I'd be tempted to attach them to a cloth or leather sleeve (either on the inside, so brigandine) or outside (scale). Depending on the size of the lamellae, it might be good to curve them or cut them into smaller pieces.

A lamellar armour with integral forearm armour (scale on leather): www.nms.ac.uk/explore-our-collections/collection-search-results/?item_id=318161

As for which side to wear a single pauldron: if you will have a shield, the unshielded shoulder, and if no shield, the shoulder that will usually be forward in your stance.

I imagine it would have probably been possible to do lamellar bracers. Trying to keep them from shifting or 'opening' would be difficult since gravity would be working on them from different directions. That's probably just me though.

As for the single pauldron? Depending what weapon you're using, it would probably be best on y our dominant hand's shoulder, since that is going to be the more forward of the two more often. As long as it doesn't block your view, at least.

I am also considering just making a Lamellar Gladiator Sleeve. That might be cool

I actually had that same thought too, that a right handed opponent might be more likely to hit my left.

And yea. Blackened steel

"Most useful" depends on the threat, and your weapon, and the rest of your armour.

What are modern threats? Mostly gun, knife, stick. Finger/hand protection from a stick might be useful, but the rest of the arms doesn't need anything. Don't bother with trying for bulletproof arm armour. That leaves knives. A full light mail sleeve with full glove for the off-hand (including palm protection):
www.hand-safe.com/Stainless-steel-arm-sleeve-with-full-hand-glove-and-Y-adjustable-Band-pd6538014.html
could be good. Rigid hand/finger protection could be good for the main hand, or mail for the back of the hand and outside of the fingers (leaving the palm open). Similar in a cut-resistant fabric might be OK.

Lightweight is important, since speed matters. Forearm armour slows you more than shoulder and upper arm armour, since you need to move any weight on your forearms further and faster. Forearms are closer to the opponent, and can be tempting targets for a knife or shortsword (but upper arm is better if you can reach).

Hands are delicate, but armour can reduce dexterity as well as slowing you down through weight. Palm armour is good for your off-hand specifically for grabbing blades, as long as it is light and flexible enough.

Hand protection can also be part of the weapon, e.g., basket hilts or enough reach to stay out of trouble.

For pre-modern threats, body and head are the most important things to armour, because arrows and spears (and sling stones, thrown rocks, etc.) can ruin your day. Upper arm/shoulder armour is important against spears and arrows, and possibly for stopping downward blows deflected by your helmet.

For fighting with knives/swords at extreme range (as one sees in duelling, especially formal duels to first blood (but armour might be prohibited by the rules)), forearm and hand protection is good. There will be a compromise between weight, protection, and dexterity - anywhere from steel gauntlets through to no armour have been chosen in the past.

The weight thing makes it hard to find historically accurate forearms and gloves. A lot of the historical stuff is under 1mm thick, which isn't thick enough to cope with re-enactment fighting. Steel armour for LARP might do:
www.gdfb.co.uk/bazuband-arm-protection-polished-steel-pair-30082-p.asp
since it's often about 1mm thick (but that's still thicker and heavier than a lot of historical hand/forearm armour).

No need to be fussy about the weight of pauldrons (unless you have to do a lot of marching). Pauldrons and light mail sleeves would be a good combination. Maybe Japanese style splinted or mail sleeves:
en.wikipedia.org/wiki/File:Kote_gauntlets.JPG
en.wikipedia.org/wiki/File:Kusari_kote_2.JPG

Thanks for the tip. What kind of lacing works best? I've seen people use paracord and it seems like it wouldn't cut as easy as leather

Paracord stretches? I never knew that. Whats better?

I'm not sure. I heard it does by one obscure source but never seen it proven