An RX 6600 should be able to slot into that case without to much issue. The right RTX 3060 or 3060 TI would fit as well. A few RTX 6700s wouldn't be too long. You just need to find a GPU that isn't over 241mm. Newegg lets you filter by size and you can get an idea of what might work: https://www.newegg.com/p/pl?N=100007709%20601292087%20601291999%20601292591%20601413215%20601297409%20601321343%20601297366%20601292759%20601295292%20601341813%20601292001%20601292002%20601292000%20601325404%20601302811%20601292005%20601293085%20601360037%20601292012%20601292006%20601296508%20601322641%20601292010%20601292007%20601292220%20601292009%20601297330%20601349675%20601301155%20601292011%20601307693%20601333783%20601399679%20601292091

The OptiPlex 7050 tower will support PCIe Gen 3 NVMe solid state drive.  The maximum speed you can expect is up to 32 Gbps or 3500 MB/s.  With that said, there is no need to spend extra for Gen 4 SSD. Although, Dell did not specified about the M.2 supported specs, the Kaby Lake processors and Intel Q270 chipset do support PCI Express Revision 3.0

to overclock you need to have a bios option to change multiplier of -k cpu (which has unlocked multiplier). Dell optiplex bios is restrictive without this option because this is a business class model. If you put same i7-7700k cpu in Dell Aurora R6 then you can overclock because it is a gaming pc line with bios and AWCC written to help user OC. In addition pc hardware needs high performance heatsink and fans to cope with high power high heat from OC. Optiplex heatsink and case is not designed to do it.  If You put a muscle car V8 engine in Corolla it is not going to work with the rest of components. bios is essential machine level code to help user manipulate cpu voltage etc during OC, it cares more about cpu engineering operation than Windows which is high level code and relatively independent of cpu spec.  both new and old -k cpu work, just old one has no record of mileage.

These Dell psu can fit 7050 tower case.  They have 6+4+4 white connector. You need to use only one of the 2x4 pin white connector for cpu in 3080. They also have 6+6 pin black pcie connectors. 5K7J8 500w Delta99TPH 500w LiteonY7R0X 500w Chicony 4FWF7 460W Chicony HG9XD 460W, Acbel 92WNC 460W, Liteon