There's a wide choice of software available for designing the components you want to make and one of the criteria to consider is what type of pieces you want to make. If you are thinking of more 'engineering' shapes that are mostly cutting out holes or pockets at fixed depths then I would suggest you look at CamBam. You can download a free trial and I've used it for years and been very happy with it. It isn't expensive and the license is pay once, upgrades for life. There's a very good support forum and many excellent plug-ins available free which significantly extend what it can do. The learning curve is not too steep.

For more arty stuff, carving bass-relief designs in particular, Vectric is the go-to product for most people. I've just got the basic Desktop version to try out. This is more expensive, especially if you want to do your own 3D designs but comes in three flavours (Desktop, Pro and Aspire) so you can work your way up the cost tree if you want to start small (no larger than 600 x 600mm) and see if you like it. There is no cost penalty for this as the upgrade price is simply the difference in the basic cost of each package. Again there are free trail downloads which, though very restricted, let you try before you buy.

Fusion 360 is free for hobbyists, extremely capable, though the limitations for non-paying users have become more restrictive recently, and it has, for me, proved difficult to learn how to make it do what I want. I've tried it and given up a couple of times and stuck to CamBam instead. Other users have much more success with it.

You can pay more for software than for the machine if you want to buy the full professional capabilities but there are plenty of us making useful stuff without having spent that much.

Kit