cache is good for making stuff run smoother, but eventually you will need to add your cache on to the drives, if you lack IO another option that should also be considered is adding more drives to the array.
ofc as a SNO generally the incoming data is much less then what a drive can optimally handle, so long as it is in sequential reads and writes.
just keep in mind, that you can in some cases add cache and end up with it having limited to no effect, due to how your data is being addressed.
generally what larger storage systems does, is bunch the drives into one big array, so that the load is shared across the different drives, instead of being focused on one or two drives out of many.
however yet again, this is very dependent of the use case, as a SNO i plan on just putting all my drives into one array, which also allows me to being to get cheaper redundancy… like say if you got two drives and needs 1 to be able to fail… then you loss 50% of your capacity for that… while if you got 5 drives and 1 redundant, then you only spent 20% of your capacity on buying that redundancy.
alas yes cache can help a lot, but make sure thats what you need… tho for running many many different things at once, then high IO is the way to go… with nvme m.2
samsung evo pro 1tb is the king of performance… tho you may make do with much much less, but do get nvme with low latency… check storagereviews if you want detailed info and many choice.