I’m running an even slightly larger setup on a Pi3. You shouldn’t be needing more than that amount of CPU and memory.
You can move the OS to a SSD if you feel more comfortable with that, but if your SD card is still wearing out there’s something to remain that’s writing too much, or it’s just bad luck (just like any SSD or HDD will crash at some point in time). Check your swap setup and the other recommendations in this post. Let alone that you should be having a backup solution in place and operation (look at Amanda in openHABian if you have not yet done so).
Now don’t get me wrong, yes I also know reloading rules is lame and there’s memory leaks sometimes.
(oh, and there’s a bug to lock the UI while processing rules which results in perceived ‘sluggishness’, too).
But you will also see that on more powerful HW (albeit maybe a little less often visible due to more reserves).
It’s a matter of software, to be resolved in software, and it won’t go away by changing boxes.