watercolor quilts are not as (daunting) as they may look- you can purchase 2" fusable interfacing grid (or other sizes- 2" is a good size for watercolors though)
quiltsmart carries the fusable grid- and i'm sure other places too- you can even purchase lightweight fusable interfacing & draw your own grid on it.
you lay your 2" (or what ever size) squares of fabric on the fusable side of the interfacing- arranging until you have it right- then press the pieces to the grid.
once the squares are fused onto the interfacing you fold one row of squares (right sides together)- go to the sewing machine & stitch your 1/4" seam- fold the next line- continue until all the rows in one direction are stitched- then fold in the other direction & stitch those rows until all rows have been stitched in place- a good pressing & you are done- ready to border (if using a border) sandwich & quilt.
you can line up pieces of the interfacing & press the edges together to create a grid any size you want it to be.
when i get home & have a chance tomorrow i will take a couple pictures of the front/back of one of my squares i have done so you can see this- there are tutorials on the technique- and you do not have to worry about sewing each of those little squares together.
i know quiltsmart has 1 1/2" & 2" grids available. some places even have flannel grids- i don't know if they are fusable or not- the fusable interfacing really makes these fun easy projects.