RAM requirements are dependent on the complexity of your design, what OS you use, what other programs you have running, and whether your RAM is shared with the graphics card. Simple designs can be created with little RAM, but you should not interpret that the minimum of 4 GB of installed RAM is sufficient for any design you may make.
Serious production work on medium to large assemblies should consider 16 GB of RAM the minimum.
Most modern cards made in the last 3-4 years should support DirectX 11. If your card does not support DirectX 11, you can use a compatibility mode but some features will not be available to you. It is strongly recommended to use a graphics card that supports DirectX 11.
If you use a 4K display (typically 3840x2160 or similar), 4 GB of Video RAM (VRAM) on your video card will likely be required, based on your designs. 6 GB of VRAM is recommended for 4K displays. If you do not have enough VRAM, you may experience sluggish visual performance during screen updates, for example during model rotation.
How multi-core CPUs affect performance
Recent CPU evolution has seen less improvement in clock speed (GHz) and more improvement in increasing the number of cores. Having access to many cores is great for general computing and some specialized applications, but it isn't a high priority for CAD software. Generally, the more cores on a chip, the slower each core is.
Most geometry operations will run only on 1 core - so to maximize performance you would want to buy a CPU with the fastest per-core clock speeds. Typically, this might mean aiming for a quad-core CPU with fast clock speeds (3.5 - 4.0 or higher GHz). In terms of Alibre Design only, you would want to avoid CPUs with 12, 16 or more cores as they will likely have lower per-core clock speeds.
Types of storage solutions
Older storage, aka "hard disks", run on mechanical devices that spin. If at all possible, avoid this type of storage solution. Their advantage is that they have a high capacity and are very inexpensive. They are ideally suited for backups or casual storage, for example of media files.
Modern storage is referred to as "solid state drive" (SSD), where data is stored on chips. SSDs are many times faster than older hard disks. This is very important if you open a large assembly that may contain hundreds or thousands of parts.
Use a solid state drive to store your operating system, the Alibre Design application, and your CAD files. If you want the fastest storage, research a type of SSD called NVMe M.2. An NVMe M.2 drive will make a noticable difference in your general computing experience, but any SSD will offer vastly better performance over a hard disk.