Choosing the right instance type for neo4j

Hello, I need some advice regarding choosing the best instance for neo4j.
We expect to start with 200 million relationships (around 5 properties) and 50 million nodes (around 5 properties as well).
We won't have many users for now, but we have writes to the db every hour, which will be around 10k relationships.

Our use case is around account balances, so the heaviest query will be getting the balances of all accounts. (the heaviest one will look at 150 million relationships)
The rest will mostly be around querying data by timeframe, or node. Which shouldn't be more than 10k relationships.

We would index account ids, and some relationship labels, such as type of payment protocol and timeframe.

Is it preferred to try and keep it all in memory for now?
Since the growth rate is a lot slower than the initial graph size?

Where could we start with heap and page cache sizes?

Happy to answer more questions if need.