I'm not set on the name for this new class, so suggestions are welcome. Right now I'm thinking of calling the class Ronin.
Sword-saint is probably a better fit for the role you want, and just like the Ronin, it will stand out like a sore thumb outside eastern settings.
You may try something like a Swordmaster, Blademaster, Duelist or Fencing Master it you want some degree historical accuracy.
In a western setting, most people who would earn a living by mastering weapons and wandering around (outside of soldiers and mercenaries) would
try and get employment as trainers or stand-ins for judicial duels (a popular passtime in germanic countries).
If we're talking about pre-medieval periods, maybe something like the gladiator would work.
Maybe I should drop the armor restriction.
This depends entirely on how items and amor works in your game, but consider the following:
are there any actual penalties to wearing heavier armor in your system and how significant is encumbrance
do characters parade in their fighting gear all the time, or is there a chance when they'll be forced to fight unprepared
(e.g. when ambushed, camping or attending a royal court).
You can see this reflected in the recent Mount and Blade, where each char has a set of fighting and civilian gear,
civilian gear selection being heavily restricted.
If armor boils down to a flat +defence, or armor class or whatever, most characters will want to wear whatever gives them the biggest number.
This is logical, because IRL you will want as much protection as possible, as long as it doesn't get in the way of fighting,
but it also means you will drop gambersons for plate armor the first chance you get and classes being restricted in armor selection is one way
to keep lower tier stuff relevant, so if you have a selection of clothes, robes, etc., "no armor allowed" can make the player pay more attention to what's available.
However, there is also another way for such characters, instead of just saying no to certain item types, restrict the overall weight of their gear
and once they pass this arbitrary threshold, you can remove or restrict certain special abilities of this class.