from my old Dell D19m
That Dell Tower, judging from internet pictures, doesn't look like it has the space available inside to install a handful of 3.5" disks. Any more than that and you will not be able to close it. A corsair 4000d, I suspect has the same problem.
Supermicro has several mid-tower cases that support many disks, including clean removable front mount 3.5" disks.
Otherwise for what you are asking:
- You will need some tower or case with enough physical space to at least just fit N 3.5 disks. For 2.5" ssd's they are rarely a problem, they don't vibrate and have basically zero heat so you can almost always lay them inside whatever case without problem.
- Maybe the biggest hurdle is a power supply that supports enough SATA power connectors for what you want, or getting a 1 to 2 SATA connector to power up N disks. And then have enough SATA [data] ports on the motherboard to connect however many N disks. Or get a PCIe card that gives more SATA ports.
Unfortunately, what you are asking sounds and seems simple enough at first thought. But to have 5 x 3.5" HDD's and 2 x 2.5" ssd's for a total of 7, consumer grade stuff sold on Newegg or Amazon can't do (certainly not elegantly). Instead of playing with 5 x 3.5" HHD's of whatever size it may be better and more economical to buy just one 12TB or larger 3.5" HDD now that they are available. You can do a NAS sever with just 1 x 12TB HHD and 1 x 2.5" ssd having the operating system nothing wrong with that, and have a second 12TB disk as data backup.