RAM and HD for Video Editing

The biggest problem here is that both the amount of RAM and the way the RAM is configured. In the case of your system, it may be that two unequal-sized sticks of RAM may have defaulted the memory controller to single-channel operation regardless of which slots the system builder had put the DIMMs into. Premiere is fairly reliant on memory bandwidth to begin with. With the memory controller in single-channel mode, Premiere Pro will perform worse on your PC than on most PCs that are powered by recent-gen 6-core/12-thread CPUs (whereas your i7-10700 has 8 cores and 16 threads).

And no PC with that outdated Intel UHD Graphics 630 (the very same IGP that debuted with the 8th-Gen Intel CPUs back in late 2017) will perform anywhere near as well in Premiere Pro as even a cheapo PC that's equipped with a 4-core/8-thread CPU but with an added cheapo (but newer-gen) discrete GPU such as a GeForce GTX 1050 Ti.

And looking at the Canadian Dell site, it appears that you could not have ordered that PC with more than 12 GB of RAM. Besides the 12 GB of RAM in that unequal-sized dual-DIMM configuration, the only other option would have been 8 GB of RAM in a single-stick configuration.

And since Dell will not sell you memory modules by themselves from its parts and accessories site, you will have to purchase memory modules (DIMMs) from a third-party reseller. With the RAM-stealing integrated graphics, I would replace both of the DIMMs in your newly-ordered PC with a 2-DIMM (dual-channel) 32 GB kit (two 16 GB DIMMs), and keep the original DIMMs for troubleshooting purposes.

As for storage, then yes. You will need to add a second, larger capacity (1 TB or larger) internal 2.5" SATA SSD such as a Samsung 870 EVO or a Crucial MX500, or an external USB 3.2 Gen 1x1 external storage device, preferably an external SSD. You see, Dell has cut corners on that PC by using a motherboard that's based on the Intel B560 chipset but then omitting most of the performance-oriented features from that motherboard as well as leaving USB 3.2 Gen 2 ports of any kind off of the board (therefore restricting external devices' speed to USB 3.2 Gen 1x1). So, that means that the only advantage of the motherboard's B560 chipset in that Dell motherboard is to run a discrete GPU at its full PCIe 4.0 bandwidth when an 11th-Gen i5 or i7 CPU is installed (which, unfortunately, Dell does not currently offer that PC with at this time). With the older 10th-Gen CPUs that Dell currently offers for that PC, Dell might as well have equipped that motherboard with a B460 chipset instead of a B560 chipset and save itself a few bucks.

And even if you do manage to squeeze in an 11th-Gen i5 or i7 CPU, that Dell motherboard will adhere strictly to the 65W TDP long-term setting, and will drop down all Turbo speeds to conform to the official TDP rating. Most other Intel chipset-based motherboards, including most other B560 motherboards, will run at maximum all-core turbo by default, resulting in the massive increase in the heat output (and therefore power consumption).

Are you using Intel's Quick Sync when working with H.264? Your best bet it to check your stats as seen in the video below. 

https://www.youtube.com/watch?v=cKBCzCkvBT8

This includes 2 recommendation links from Puget Systems... copied from Peru Bob
https://community.adobe.com/t5/video-hardware/premiere-pro-hardware-articles-to-read-before-you-buy-or-build/m-p/11557686

Moved to the Video Hardware forum.

See here:

https://www.pugetsystems.com/recommended/Recommended-Systems-for-Adobe-Premiere-Pro-143/Hardware-Recommendations

Adobe Premiere Pro CC System Requirements