This has been the agreed-upon way to do things within the MS umbrella for a while. Not sure why they won’t just allow for setting a higher rate limit.
Each app registration in a tenant gets their own limits. Most backup platforms for an MS tenant have you register 4-10 apps so it can parallelize the backup load without getting rate limited.
Should be supported. If you’re already running a 5000 series CPU, there won’t be any issues swapping in another 5000 series.
The only time you run into issues is if you were previously running a 1000 or 2000 series CPU and need to make the jump straight to 5000 series.