Special Considerations for SQL Server with 512 GB RAM / 64 Cores? Apart from some Windows Hotfixes are there any special considerations (i.e. "things to worry about") when running SQL on a server with 512 GB RAM and 64 logical cores?

I'm aware of some guidance when operating above one or both of these thresholds but not right at them.

OS: Windows Server 2008 R2 
SQL Server 2008 R2 SP3 (clustered)
Max Server Memory should be no higher than 445 GB. This gives Windows enough memory to manage itself. Yes, it really does need that much.

Max Degree of Parallelism should be set to the number of logical cores in one NUMA node, up to a maximum of 8.

If it's running an OLTP environment, make sure Optimize for Ad Hoc Workloads is enabled.

Ensure power saving on the OS is set to High Performance.

TempDB should be on your fastest storage, followed by transaction logs.

There's a whole lot more you can look at, but these are the main items.

As some comments have noted, SQL Server 2008 R2 is out of mainstream support. Extended support ends in July 2019 (not this year), so there's just about enough time to start a project to move to a newer version. I would be looking firmly at SQL Server 2017 or later.