A lovely big project - the design is worked in pure cross stitch with backstitch detail. The carnation border is worked in just cross stitch with the flowers embellishing the sampler embellished with backstitch as necessary. I suggest all the backstitch writing is worked in dark grey with the remaining outlines worked in the darker shade within each motif.
To work out the design size (or the stitched area) you need to divide the stitch count by the number of stitches to the inch (2.5cm) on the fabric. You then add enough fabric to this measurement to allow for framing etc. If a stitch count is not shown on any design, you will need to count across the design and down the design, which will give you the stitch count.
Example: 140 stitches divided by 14 (Aida) = 10 inches
If working on evenweave fabric, remember that you generally work over two fabric threads, thus 28-count linen is also 14-count when doing the sum. I suggest adding 5 inches to the design size on a project to make sure you have an adequate margin for mounting and framing. Obviously you can adapt this amount when working a small card of lid top.