Optimising MariaDB for large AWS machines
innodb_buffer_pool_instances will not give you a huge advantage unless you are suffering from a very specific write contention between multiple write threads. I have personally never needed to increase it over the default 8 instances.

I use 500GB servers for MySQL and dedicate around 384 GB to the buffer pool- more would also make sense - I optimize for huge concurrency and even then I am thinking to increase it to an 80% or 85% of the total available memory (but want to leave enough for the filesystem cache).

If that would be an advantage for you or not, it will depend on your access patterns- if you are doing analytics queries, your speed up may be minimal- and of course it has decreasing returns to the point of not being an advantage at all for memory larger than a dataset.

It is very difficult to provide a general advice, but if I had todo it would be this: 1) make sure you are using the right tool (vanilla mysql-InnoDB- may be not a great a great tool for analytics- plugins or external tool may fit better); 2) keep 10-20 percent of your data on memory (most needs follow a 90-10, or 80-rule for frequency of access; and 3) keep your buffer pool with a 75%-80% of your total memory if you only use InnoDB as your main engine. Stress on general advice, your needs will vary and so your configuration. See what is your bottleneck and try to optimize that.