If you haven't already, consider joining the "Brotherhood of Red" Facebook group:
https://www.facebook.com/groups/178433162242769/There are active discussions regarding red fighting as well as several resources.
To answer your questions
"Got after the legs." - How do I do this without making my extended arms targets? The legs are far away so I must extend my arms to reach them unless I want to be within easy striking range from even the smallest blue.
Are you keeping both hands on the handle when attempting to hit these targets? One important technique to master as a red fighter is referred to as casting (think casting in reference to fishing) where you use only one hand on the weapon and use that extended range to target extremities especially legs.
"Go after the arms/shoulders." I can't seem to clip them. I don't get how to go after a shoulder aside from waiting for an attack or drawing them out with a feint, which no-one ever buys.
With no shield to hide behind, you'll have to utilize your mobility and footwork to put yourself in a better position to target the arms and shoulders. You can also target the outside of the forearms with downward or casting shots.
"Making every shot a kill shot." I've heard this many times and it frustrates me. Shield. There's a big shield right there. It's in my way and moves faster than I do around a smaller radius. And no I don't have the power to move the shield sufficiently and still have enough fore to count as a hit.
The logic behind this is that it takes at least two (assuming the shield fighter considers the red shots acceptable) hits before you can actually get to the fighter. Admittedly, the shield is a big target but it really shouldn't be the one you should be going for unless you don't have any other options. Ideally, you would be using positioning, mobility, feinting, and baits to make the fighter move the shield and open up a vulnerable spot. Also, many shield fighters are willing to soak that first red shot and charge you (It's what I normally do.) to get inside your range.
Mine is only one perspective. I would suggest you post the questions in the FB group to get more varied responses.
"...change requires action, it doesn't just happen. Define your actions by how you think the game should be, not how the game is. The game will follow."--Big Jimmy