Both your practice piece with the lovebirds and the peacock are really dynamic and unique for a wholecloth design. I would almost be tempted to do the lovebirds as hand embroidery in colorful embroidery threads and just quilt background fill like mctavishing in a matching color.
I have seen some amazing wholecloths at shows that used colored thread to make the design and they were spectacular. There are examples pictured in this topic:
MQX Show, Tons of pics
Also in that same topic are some pics from Irena Bluhm's booth, she quilts then goes back and colors in using colored pencils. That is another approach you can take.
I do love the look of quilting with high contrast colorful threads, especially on black or dark backgrounds. The upside is it makes a dramatic and dynamic presentation but the downside is every wobble and missed backtrack really stands out. If enough thread is laid down, it helps to not notice that so much.
Another technique I want to try is Graffiti quilting which Karlee Porter developed and teaches
https://www.karleeporter.com/2015/08...-crash-course/ . Just search images of it and you will see examples. This style can be done with heavy threads or regular threads. Wonderfil threads makes a 12 wt cotton called Spaghetti you can run through your machine. But when quilting with such heavy threads you will need to preplan your thread path carefully because backtracking would be very unforgiving and you would want to keep it minimal or try not to do it at all.
I really think you need to experiment to see what you like best. I really think that peacock would be very dramatic done on a dark background with colored threads. I think I would keep it wallhanging size. Nothing larger than say 50" x 60" but that is JMHO.