Valerie, i recommend you start with something you enjoy, simple, and of the typical size you most often cook. A steak or two, or a few pieces of chicken for example. Your first cook is not the occasion to make a roast beef dinner for your entire family.
All the help you will need in understanding your new cooking technique is revealed at Dr. Duglas Baldwin's site. Start there before you cook anything.
You might want to have two containers. You probably already have a stock pot that will be just fine for most of your sous vide cooking. Something larger, up to 20 quart capacity will allow you to cook large items, spare ribs and roasts for example, and larger quantities for those family lunches.
I have two more suggestions for you.
First, keep a detailed record of every cook starting with your first. I recommend recording the menu item, its thickness not weight, the temperature, and length of time you cooked it. You will find it helpful to also record the outcome and any recommendations to improve on your results. Doing that will enable you to precisely replicate all your successes and improve on your almost successes.
Second, the SV cooking technique is significantly different from comventional cooking. You will need to break with most of your past cooking practices because they don't apply in low temperature water bath cooking.