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If the question is to run 10x5TB nodes or a 50 TB node made up of 10x5TB drives, then my suggestion is to run 10 nodes of 5TB (with each node being a single 5TB HDD). My reasoning is that with 10 HDD drives acting as a single node then the chance of losing a drive and losing your entire node is far worse than having 10 nodes and only losing a single node.
Remember, payments are based on node reliability and it takes months for each node to get a good reputation and become profitable. Here is a good post on profitability:
As Storj just recently went into production status the demand for storage by paying customers is just starting to grow. If you put together 100TB of storage who knows how long it would take to be used? To lower your risks you might want to start with a few lower cost HDD drives and add nodes as you fill each node. Also due to the need for reliability consider quality disks, reliable networking, power backup.
My personal experience is that I started with a single 10TB HDD (Western Digital ‘Red’) which is consumer class and as it filled up and I learned more about Storj, I decided to add 14TB Western Digital HC530 HDDs (Data center class drives that are designed to run 24x7 with low power consumption). Also remember you lose about 10% of your capacity for headroom so I get about 13 TB per drive. My breakeven for one 14 TB drive is about 15 months and 19 months for two. We are in it for the long game.