Dutchman, if you go to Pro Landscapes site, you can order a demo of their product and the sales staff is very good about answering questions. You can call or email them and they will answer immediately or get back to you quickly. I'm sure if you asked, they would be able to give you the real number for their plants in your zone. How do you intend on using the software?
You had better do a great deal of design work and be paid very well for it to purchase, maintain and print software. Software does not make designing easier, but does offer people with better computer skills than drafting skills a professional looking drawing. I do not find the "drawing" takes a great deal of time, but the designing does. A CAD based program is a digital pencil, and if you are better using the computer than pencils and paper, go for it, but weigh all the costs.
drsogr, with your skill and experience, drawings with CAD may be simpler and easier. For larger work you may want try creating your base plan with the CAD, printing it out and creating the concept by hand and then going back to CAD to create your final drawing for presentation. If you do mostly smaller designs, you may be able to do it all from a computer. I'd like to get some tips and trick from you if you are able to do a foundation planting in 45 minutes, but then again, I coudn't justify my price for design work. I usually spend about 10 hours on the front of a mid size home with drawings, plant lists, materials and construction notes, imaging and presentation. The 3D imaging isn't drawn, it's using an imported photograph and pasting plants, hardscapes, mulch and other landscape features as a visual representation of your design with the clients home or property as the background. Imaging is relatively quick and easy if you already know what your design is going to look like. It makes a great presentation tool to use with clients on larger projects. when they are parting with tens of thousand of dollars or more, usually they want to better understand what it's going to look like. They really aren't as interested in your style as much as their are concerned with getting what they want. When you can show it to them in a way that is easy to understand, most clients are willing to give you a budget that that more easily accomplishes both goals, your and theirs. You are very wise to use a designer or more than one. That let's you concentrate on what you do best and bring in someone with specialized knowledge and abilities only when needed.