Most water bath canners are made from stainless steel (commonly 201 or 304) or enamel-on-steel, which consists of a durable steel core coated with a porcelain enamel finish.
Yes. Many canners double as large stockpots for soups, stews, pasta and general cooking; some product descriptions explicitly state the canner can serve as a stockpot or be used for other cooking tasks.
Jar capacity varies by model. Across these listings the ranges are approximately: 4–15 quart jars, 7–18 pint jars, and 7–13 half‑pint jars; many mid‑size canners commonly list capacities near 7 quart jars or about 8 pint jars.