Hi Lisanne
Welcome from upstate NY (near Vermont). Wow you have quite the ambitious project planned! Good for you. My first quilt was a sampler as well but I made it from a book that was geared specficially to teach beginning quilters so all blocks were already designed and templates in the book. the book even planned the placement of the blocks. Thankfully I took a beginner class to make 4 blocks and introduce me to rotary cutting techniques so I only used the templates on odd shaped blocks like friendship star and LeMoyne Star and curves and the few applique pieces in the sampler. For the rest of the traditional blocks I just measured the templates and cut away with my ruler and rotary cutter for all the other blocks. LOL, I still have that book and every single template is marked with sizes for strips then cutting the stips down to HST or whatever was needed.
I have never drafted out my own blocks except for a mariners compass and I did that full size because I used the drafting pattern to create the paper pieces for paper piecing. Other then that, I have only designed a quilt using blocks that I had a pattern for. There is a great website that has lots of free block patterns. Here is a link
http://www.quilterscache.com/QuiltBlocksGalore.html
Regarding color... that is a personal choice. I have made a baby quilt sampler that was scrappy, all different colors and my planned sampler used 4 or 5 different fabrics but had an overall feel of dark green and brick red. Both looked great. I think you will know after you have completed a couple of blocks and laid them out if you want to do the whole thing scrappy or choose a color theme. Can't wait to see pictures.
FF