Your machine is pretty adequate in terms of processing power (unless you shoot in medium format). 8Gb of RAM should also be quite enough if you don't run another heavy app in parallel.

Depending on the size of your catalog you may or may not notice a big difference when moving around catalog and cache. But, since Lightroom catalog is comprised of lots of small files and folders (in total about twice as there are images), there can be a noticeable improvement using SSD. This is due to faster file system access coming from less latency and no fragmentation effect which might be there for HDD.

Anyway, I just did a test of having a catalog of about 40K items located on HDD versus SSD. The images themselves are on another drive so their location is not a factor.

While having the catalog and cache on HDD (RAID1 of 2x7200rpm), ready time of Lightroom (when all of the imported folders display their number of items) is about 3 minutes. This is on cold start. When restarting Lightroom, it is ready almost instantly which is an effect of available RAM.

When the catalog and cache are on SSD, the cold start time is maybe 2 seconds.

So, placing your catalog and cache on the SSD would be the best way to improve cold start performance. Since your previews only take 10Gb, I'd say it is not critical to limit the cache storage size yet.

The effect of limiting the cache size is that the least recently accessed items get deleted when newly accessed items needs to be cached. That's fine if you mostly look at the same or new images, but if you browse more randomly, limited cache will not do much for improving the performance.

Tangentially, having more RAM would make it easier to browse back and forth while having more processing power would make it (slightly) faster to import new images and do the processing.