Actually, I think your best bet is to buy a series that includes a variety of workouts and which you can use to create your own workout sequence throughout the week.
I would start with the Body Blast series. It includes a full step routine, Step Blast, which is one of Cathe's best in my opinion. It includes a circuit workout, both on and off the step, where you can do as little or as much of it as you want. It includes Cathe's best kickbox workout ever, Kick, Punch, Crunch, which is paired with a weight training workout that focuses on all the muscles of the lower body and is extremely thorough, Legs & Glutes. It also includes 2 weight training videos for the entire body, Push Pull and Supersets, which is great fun with fabulous music.
In this one set you have everything you need to start off on your fitness journey and as an introduction to Cathe. Then you can move up to the slightly tougher Intensity series (which includes the Pyramids) and from there, onto the toughest: the hardcore series!
You will need a barbell withnplates that take yo up to about 60-70 pounds. There's a good, cheaper one available through walmart.com and the Troy Lite system from Fitness first, online, which is one of the best since the bar itself is light and the spring clips are so easy to handle. Even though you won't be using all that weight at first, as you gain strength, you will want to increase your range. You will also need a range of dumbells, from 3 to 10 or 20 pounds. Again, you can buy these in increments as your strength increases. Start with 3s, 5s, 10s and 12s and add on from there. Also, a stability ball, which you can get very cheaply from TJMaxx stores and other sporting goods stores, like Dunhams.
Have fun!
Clare