I agree with SimplSam: splitting the art into two pieces gives you the most flexibility for posing. Fortunately, Moho makes it easy to do this.
The sleeve design intrigued me, so I hope you don't mind that I used it to create a 'cheap' version of a two-piece setup...well, okay, three pieces...
Here's the setup: First, I drew the whole arm as one layer, and I split the elbow area into two shapes with a hidden shared edge...
...then I duplicated this layer, named it ArmLoL, and knocked out the shapes I didn't need in this layer. Like so...
Then I made another duplicate of the original and named it ArmUpL, and knocked out the bits I didn't want in that layer...
I kept the original full arm layer and moved it outside the rig, and hid it. This version is kept as a backup. The third part is the shoulder, which I kept outside of the arm group so I could move it in front or behind the arm group.
Normally, I would make a Smart Bone Dial to control the sorting of the layers, and instead of having it shuffle the layer order, I prefer to make duplicate or reference layers of the limbs around the body and animate their visibility. This is because I want the flexibility to change the rig when needed, but animating Layer Order with a Smart Bone locks me into only what the Smart Bone allows. Animating visibility with the Smart Bone Dial means I can insert new layers and move layers around manually without breaking the Smart Bone Action.
In this demo rig above, however, I'm just manually moving the layers up and down the stack where I need them. For simpler rigs, this is my default method...it's easy enough to set up, easy to animate, and anything more is just overkill to me. Tip: use
Timeline Visibility to keep the animated layer order keyframes visible when animating other layers.
The only Smart Bone in use is for the lower arm bone. This is used to change the curvature inside the elbow to a crease and to make the outside more rounded.
Anyway, if anyone cares to look at this demo file, it's here:
armRigDemo_B_01.zip
If this rig were for production use, I'd make the 'roll' around the shoulder smoother, improve the elbow bend, and maybe add a proper fold line in the elbow. Oh, and Shy the elbow bone because you don't want to keyframe that. But this is a good example of how you can seamlessly split a limb to wrap around itself and the rest of the body pretty easily in Moho.