Welcome to the board. You will always get answers to questions here.
I'm sure others will comment on your question also but it seems you have your estimates about right if I understand your plans for each quilt. For the Dresden plate are you getting FQ's or 1/4 yd pieces of 20 fabrics--that should be plenty if you are doing them scrappy. For the Irish Chain, the light always takes more than the darker chain. For the sampler,a good rule of thumb is to calculate the total yardage and divide the number of different fabrics by that and get a little more of each fabric depending on how complicated each block will be, more seams take up more fabric. Have fun on your shopping trip!