This is mostly for my own reference but other people might find it useful, so I'm leaving it public.
A general note about plate armour - a full suit of high-quality, articulated plate armour of early 16th century would weigh around 60lb. Heavy, yes, but still less than what many soldiers carry into combat today. (In Bravo Two Zero, eg, Andy McNab mentions that his SAS team carried around 200lb each.) Chances are good that Arthur's been wearing armour since he was a teeny sproglet, so the weight and slight restrictions on mobility would be second nature to him.
Most of Arthur's plate armour is early 16th century and fairly generic 'European'. He combines it freely with mail, which was more common a century or two earlier.
Head
Arthur wears a barbute, a 15th century Italian form of helm that was usually worn by infantry. Under it, he sometimes wears a mail coif, separate to his hauberk.
Neck
Arthur's plate armour leaves his neck very unprotected as his gorget starts a lot lower than they did historically - they would normally come about halfway up the neck or even higher, where Arthur's barely reaches the bottom of his neck. However, the neck of his coif provides some protection, as does the low edge of his helm.
Arms
On his sword arm, he has a pauldron (shoulder), rerebrace (upper arm), couter (elbow) and vambrace (lower arm). He also wears a very short vambrace on his left arm. He wears leather gloves. Let's assume they have some form of mail or plate in them because otherwise, OW.
Body
A short-sleeved mail hauberk over a padded gambeson. Typically 12th century.
Legs
No armour.
Sword
This is a tricky one, and I confess I could know an awful lot more about swords than I do. However, based on the fact that it's double-bladed, straight-edged, hollow-ground and fullered, with a point, I'd say it's some form of longsword. Which makes sense considering the kind of armour that's around. The hilt looks very short to be a one-and-a-half-hand (or bastard) sword, but that's definitely the fighting style he uses. (Right hand on the hilt, left hand on the pommel to provided added strength and direction.)
Shield
Straightforward heater shield. Typically made from several layers of thin wood, overlaid with leather. (Heater shield is a modern term. I have no idea what they were called at the time.)
Dagger
When wearing armour, Arthur doesn't carry a dagger. This makes sense because the dagger was used to parry your opponent's sword as a last line of defence. Armour takes over this role, while leaving you with a hand free. However, when he's not wearing armour, he carries a quillon (or sword-handled) dagger. (Which means that he's always prepared for a serious fight and that makes me happy in my pants.)
When he first appears, throwing daggers at the peasant-powered moving target, he's using rondel daggers. They have a more even weight distribution than a quillon dagger, which would probably make them easier to throw, but it's not something they were especially designed for.