Mismatched dinnerware looks curated for about five minutes and then it just looks like you never finished unpacking after a move. I'd rather have a plain, boring, complete set than a cabinet full of charming orphans, because the plain set actually makes dinner feel like dinner. One good set beats a hundred cute singles every time.
Stick with colors you won't tire of by year two: white, cream, a soft stone, maybe a dusty sage or warm terracotta if you want a little life in there without committing to a whole mood. White is the one to start with if you own nothing, not because it's safe but because it lets the food and the table linens do the talking, and it plays nice with whatever glassware or napkins you pick up later. If you want one bold thing, let it be the serving bowl or a stack of side plates in a color that makes the white pop, not the whole set. A well made plate has some weight to it without being a dumbbell, glaze that's even and doesn't pool at the rim, and a foot ring that's actually finished smooth, not sanded roughly so it scratches your table. Run a thumb around the edge in the shop or on the product photos if you're buying online. Cheap stoneware chips at the rim within a few months of normal use, and once one plate chips the whole set starts to feel shabby even though the other eleven are fine. Porcelain and well fired stoneware hold their glaze and their edges through the dishwasher, through a toddler dropping a bowl of cereal, through a move where the movers wrap everything in one towel and hope for the best.
For sizing, measure your table and your cabinet before you fall for a set online. Dinner plates in the ten to eleven inch range fit most tables without crowding, but if your table is narrow or round, drop to the smaller size or you'll be playing plate Tetris every time you serve a side dish. Check your cabinet shelf height too, nothing worse than a gorgeous set that won't stack under the shelf above it. The real mistake people make is buying a huge matched set for daily use and nothing extra for when six people show up, so get a core set for the everyday and a few extra bowls or plates in a complementary finish for when the table grows. Buy enough that losing one or two to chips over the years doesn't wreck the whole set.
A good set should survive a dishwasher cycle, a dropped lid, and a house move without you noticing it happened.