See my response to this post, try reversing translate() and rotate(), then ask if you have more problems.

" I have the former working nicely"
Good! What is the problem, then?

" but am stuck otherwise"
Stuck where? What is "otherwise"?

" Is it best to"
The "best" way is the way working as you want...
Sometime, you have to do a translation, rotation then translation, particularly when you want to rotate at a given point of a shape.
Otherwise, translate() then rotate() is enough.

Demonstration:

1. int shapeW = 150;
2. int shapeH = 100;
3. 
   
4. void setup()
5. {
6.   size (600, 600);
7. 
   
8.   smooth();
9.   noStroke();
10.   ellipseMode(CENTER);
11. }
12. 
    
13. float angle;
14. void draw ()
15. {
16.   background (255);
17. 
    
18.   // Do the rotation
19.   rotate(radians(angle++));
20. 
    
21.   fill(#00AA00);
22.   // x, y always 0 since translations do the job of placing
23.   rect(0, 0, shapeW, shapeH);
24. 
    
25.   // Mark the rotation point
26.   fill(#FF0000);
27.   ellipse(0, 0, 8, 8);
28. 
    
29.   // Mark the bottom-rigth corner
30.   fill(#0000FF);
31.   ellipse(shapeW-1, shapeH-1, 8, 8);
32. }

The rectangle rotates around its top-left corner, in the top-left corner of the sketch.
Now, let's rotate the shape in a point a third of its width / height:

1. void draw ()
2. {
3.   background (255);
4.  
5.   // Do the rotation
6.   rotate(radians(angle++));
7.   // A translation to change the rotation point in the shape
8.   float rotX = shapeW / 3;
9.   float rotY = shapeH / 3;
10.   translate(-rotX, -rotY);
11.  
12.   fill(#00AA00);
13.   // x, y always 0 since translations do the job of placing
14.   rect(0, 0, shapeW, shapeH);
15.  
16.   // Mark the rotation point
17.   fill(#FF0000);
18.   ellipse(rotX, rotY, 8, 8);
19. 
    
20.   // Mark the bottom-rigth corner
21.   fill(#0000FF);
22.   ellipse(shapeW-1, shapeH-1, 8, 8);
23. }

You can then do the rotation anywhere in the sketch:

1. void draw ()
2. {
3.   background (255);
4.  
5.   // Move the origin to the point where we want the rotation to occur
6.   translate(width / 3, height / 3);
7.   // Do the rotation
8.   rotate(radians(angle++));
9.   // A translation to change the rotation point in the shape
10.   float rotX = shapeW / 3;
11.   float rotY = shapeH / 3;
12.   translate(-rotX, -rotY);
13.  
14.   fill(#00AA00);
15.   // x, y always 0 since translations do the job of placing
16.   rect(0, 0, shapeW, shapeH);
17.  
18.   // Mark the center point
19.   fill(#FF0000);
20.   ellipse(rotX, rotY, 8, 8);
21.  
22.   // Mark the bottom-rigth corner
23.   fill(#0000FF);
24.   ellipse(shapeW-1, shapeH-1, 8, 8);
25. }

You can put the rotation point outside of the shape:

1.   float rotX = -shapeW / 3;
2.   float rotY = -shapeH / 3;

And so on.