What exactly does the character value "Restriction" (affected by gear) do? The description in the manual wasn't too helpful...

Each weapon has a maximum "restriction". If it is exceeded, the "hits accuracy" is reduced.

I just read the manual again and realized it affects attack speed, attack rating and defense. I could also verify that in-game. As you mentioned it is also a limit on what weapons you can equip, and high restriction also leads to higher mana cost for spellcasting.

I don't know if the following is all restriction does but every 10 points of restriction increase the "attack speed" rating by one (lower is better). So what you can do is learn all the restriction lowering skills from Mudam and Lucan and put together the best armor that won't raise restriction beyond 9 (or 19, 29 etc. if you are willing to sacrifice some attack speed)

When I played this back when it was new, I found the attack speed to be the single most important melee stat, though - if your attacks are a good deal quicker than your opponent's, you can lock him in a staggered state, thus denying him any chance to attack you.

Maybe instead of "restriction" it could have been said "hindrance" or something like that.