You've got a good list there of designers. I would suggest you get a few pantos first as these are the money makers, they can be stitching away whilst you custom quilt on another machine
.Types I use the most-
Open and swirly
Swirly and spikey.
Some pantos are rectangular in shape and can look as if they are sewn in rows. Where possible I prefer ones which interlock between the rows but if you want to make the design more open you can run tight on throat space with these.
Because you are so good at free motion you may find custom quilting is not so fast with a computer system as working freehand so may not need lots of motifs to fit into blocks but border designs can speed life up. You can also use pantos in borders.
Like fabric and thread it is easy to get carried away with your purchasing but remember you can buy the design and be stitching it within minutes at any time of day so you don't need to get lots in advance. Sign up to the sites and they will send you notice of special offers and sales.
Yvette in the UK