You will need a support for your painting, and rather than make it yourself (what I normally do), you may want to go and buy a pre-primed gessoed Masonite board for expediency. The reasons for a hard support as opposed to canvas are many, not the least of which are longevity, durability, and more control. If you absolutely need canvas, make sure to choose a fine linen weave on board, rather than on stretcher bars.
You can buy an 18″x24″ Ampersand Gessobord, uncradled 1/8″ flat panel, at Utrecht for about $17. It is a sealed hardboard panel with an acid free, acrylic gesso ground that you can start using right away. Or, you can buy Utrecht’s excellent cradled, 18″x24″ unfinished wood panel and gesso it yourself for about the same price.
Buy the best marble-inclusive gesso from Frank Covino. If you gesso your own, make sure you protect it on the back as well so that it cannot absorb moisture and warp. To save on the cost of expensive gesso and to give them a clean, fresh finish, I coat the backs of my boards with oil-based Kilz, a fabulous and reasonably priced protectorant/primer/sealer, then apply gesso on the front only.
Decide on the size of board, based on the Old Master work you have chosen. For example, for most lifesize portraits on a 16″x20″ panel, the figure will end at the armpits. A size approximating life is best, as a giant head can look grotesque–unless that’s the effect you want to achieve. Keep in mind the following parameters for face sizes on the panel–smaller than life is fine but these are LIMITS you should not exceed:
babies: 5″ from chin to hairline
children 3-12: 5 1/2″
teens to age 27: 6″ maximum, male or female
adults: 7 1/2 for men with large heads, 6 1/2 for women with large heads
The other item you will need right away is a 9-value (plus black and white) palette–more about that tomorrow.