If you increase RAM on your current computer, the elapsed time to wait for the solution will be reduced on large models, but will have no effect on small models. On a structural model, under Analysis Settings, Solver Controls, set the Solver Type to Direct. You can easily tell if the solver is running entirely in memory by looking at the solution output. Click on the Solution Information folder in the Outline and the Worksheet will show the Solver Output. Click on the text and type ctrl-F to search for allocated.
You can see that the model above was allocated nearly 14 GB of available RAM and ran entirely in that memory block.
A much larger model will show this note.
You can see that the model above needed 283 GB to run entirely in RAM and that was not available, so the solver will use the storage to hold parts of the matrix while it is computing the solution.
2. The memory limits the number of grids, the CPU limits the calculation speed, and at the same time, the memory speed may affect the calculation speed.
The example above shows that the memory didn't prevent the solver from running, it just affects how it runs. Running out of disk space will prevent the solver from running.
Your proposed computer configuration shows only one SSD. You want to configure the solver to use that drive while solving. The simplest way to do that is to store your model there. But if that is the C: drive, the installed programs use up some of that space leaving less available for the solver. You don't ever want to run out of disk space during a solve. Another issue with having only one SSD is the Windows OS needs to write files to the disk at random times, therefore, it is optimal if Windows is writing to a different drive than ANSYS. That is why I recommended two SSDs. One for the C: drive, which could be 256 GB, and a second drive, 512 GB, just for ANSYS models to solve on, while the third HDD is for moving old models from the SSD to the HDD so you don't run out of disk space on the SSD during a solve.
If you leave Solver Type to Program Controlled, ANSYS may choose the Iterative solver instead of the direct sparse solver. The iterative PCG solver might solve the same model in more or less time. If you are going to be solving almost the same model many times, say in a parameter study, you may want to solve the exact same model twice, once with Direct and once with Iterative. Scroll to the end of the Solution Output and note the Elapsed Time for each solution, then you can select the solver that took less time for the rest of your study.