We are in process of designing the infrastructure architecture to host sitecore 9 update 2 in azure. This requires us to appropriately size all the databases for Sitecore 9. Also I can't find any good documentation on whether if any of these DBs needs to be single-database vs. elastic pool.
Marketing Automation database
Reference data database
Shard map management
Shard 0/1 databases
The site will be multisite and visit's per month will be around 500,000/month. I had a look at this KB below but I can't figure out which DBs should be in elastic pool. https://kb.sitecore.net/articles/267409