OK, lots to unpack here :-)

Firstly - a lot depends on the plans for the server. If it is to *solely* run Oracle SE, then having a large surplus of cores is just a waste of money. Of course, if that server is going to be used for other purposes as well, then those extra cores can be put to use elsewhere.

Lets assume you're going with one box and its only going to run SE. So I only "need" 16 cores, but in reality, I'd want a few more than that because no machine (irrespective of architecture) runs great when its totally maxed out near capacity. Hence you might look at something with (say) 24 cores. Alternatively you could look at a 2 socket machine with 12cores each, because that gives you some redundancy should you lose a CPU, and the lower the core count, typically the higher frequency you can run the CPU at.

On that topic, I would want the absolute fastest CPU's I can get because its not like having more cores and more threads gains you performance, because we set that hard limit at 16 "cores worth" of work anyway. The challenge here is the definition of "fast". Yes it includes frequency, but things like L1/L2/L3 cache sizes and the type of memory supported also play a roll here, so you should take that into consideration as well. For the vast majority of Oracle workloads, niche CPU features like floating-point performance etc don't really gain you much, because almost all Oracle computational work is memory access/update and integer arithmetic. So its all about high frequency and fast memory access.

Having said all of that... the easy way to deal with all of this is run on a cloud system. Choose a nice low base CPU number, and then flick the switch on auto-scaling so you can handle the peaks, but for most of the time you're using the bare minimum amount of CPU (even less than 16 threads).