Hello [NAME] , the precision 5810 and 5820 seem like good choice.  They both have 6 SATA ports onboard.  The 5820 has more space for 3.5" drive configuration than the 5810.  Both models can run multi NVME SSD drives via ultra-speed adapters and flexbay backplane (5820). Depending on your budget, find a system with the base configuration of what you need and work on the expansion later.  
I have a T7500, T3600 and some 3 x 9020 and have used them all okay with video editing.  I haven't had any real problems with any of them although I mainly edit in HD not 4K although I have dome some still with problems. Whilst that is the case I am looking to get a more modern rig to replace the T7500 but I am not sure what to get..   Due to economics I go 'used' and am looking at the models 5810, 5820, 7610 as they seem to be more available in my price range. I see the CPU E5-1650 v3, 1660x4, 2620 but also not sure what is the better. It needs to hold 4 HDDs as the T7500 does. I know it is maybe Mickey Mouse to some, however price keeps me in this ballpark. Could I get some ideas about choices please. I could go out of the Dell sphere but if possible will stay. Thanks    
Help selecting Desktop for basic video editing.