I have ridden many turn overs of cassettes put together on my own. As wear progresses, I replace only individual cogs. I found it beneficial to stock spacers of different thickness that allow to compensate for variations in characteristics of cogs. There is a guy on Ebay who makes cheaply custom spacers, of any thickness you desire. Otherwise, I found than an Sram ESP rear derailleur is more tolerant to variations in the cog spacing, than a derailleur following the Shimano standard.