Download Windows 10 Disc Image (ISO File) Microsoft site

Download Windows 10 Microsoft site

Whichever link works better for you.  I did the first one last year.

Then DL all the drivers, etc., from Dell's site?
What about the product key? Will that be an issue? I don't ever remember having a problem with that when I've used the OS recovery tool in the past.

As long as it already had Win10, product key is imbedded in BIOS.  Win10 automatically downloads/loads correct drivers for the PC it's in.  I transferred an SSD with Win10 last year from Optiplex 7010 to Precision 3620 without any trouble.  Exception if one reloads, programs, printer drivers, any other special item drivers, may still need to be reloaded.

If by chance you're still missing any drivers, then yes, use Dell site or Dell Support Assist.

Something to strongly consider is go from an HDD to an SSD instead.  Or a new HDD at bare minimum.  Your current HDD may have failed and that's why it crashed and won't reload.  One way to check is turn on PC and immediately and repeatedly press F12 for Boot & Diagnostics menu.  Run diagnostics.

I don't know how old the 7450 is.  If it's 5+ years old, replace or test the size 2032 CMOS battery.  Bad batteries affect BIOS therefore affecting system operation.  Booting problems typically occur and so does reloading.

First off, I uninstalled the OS recovery tool, along with a plug in for it, that was related to Dell support assist & then reinstalled the OS recovery tool.
I kept a closer eye on it this time & happened to catch it right as it finished, I started verifying image & the program quit, Looking in event viewer, I see two errors, The first contained the following info;

Application: DellOSRecoveryTool.exe
Framework Version: v4.0.30319
Description: The process was terminated due to an unhandled exception.
Exception Info: System.NullReferenceException
   at Toqe.Downloader.Business.Utils.HashHelper.FinalizeHashBytes()
   at Toqe.Downloader.Business.DownloadManagerAPI.IndividualDownloadHandler+<>c__DisplayClass43_0.<StartConcatThread>b__0()
   at System.Threading.ThreadHelper.ThreadStart_Context(System.Object)
   at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)
   at System.Threading.ThreadHelper.ThreadStart()

And the second contained this info;

Faulting application name: DellOSRecoveryTool.exe, version: 2.3.7523.0, time stamp: 0x6544d7b2
Faulting module name: KERNELBASE.dll, version: 10.0.19041.4412, time stamp: 0x6d8c3da8
Exception code: 0xe0434352
Fault offset: 0x00140b82
Faulting process id: 0x10b44
Faulting application start time: 0x01daaa65825b5765
Faulting application path: C:\Program Files (x86)\Dell\OS Recovery Tool\DellOSRecoveryTool.exe
Faulting module path: C:\Windows\System32\KERNELBASE.dll
Report Id: 7f656b54-59f8-485b-9354-00a698c5137b
Faulting package full name: 
Faulting package-relative application ID: 

Any suggestions?
Is there a place (or way) I can DL the ISO & then use Rufus to create the bootable USB?

But your Exception code: 0xe0434352 is a .net framework exception. Honestly would be more work to track it down than making a generic Windows restore disk and rebuilding off that. 

Rufus isn't needed to make a bootable USB, and some don't always have luck doing it that way.

On a working PC, you will be downloading Win10 to an 8GB or bigger blank flash drive formatted to FAT32.  They often come formatted that way anyway.  https://www.microsoft.com/en-ca/software-download/windows10ISO  Download the ISO.  It will be in your Downloads folder.  With flash drive inserted, click on the ISO and follow onscreen instructions   Win10 will then be loaded on the flash drive.  Takes a little while.  When ready to load Win10 from flash drive, boot from from flash drive on your PC to load Win10.

When a window pops up asking what partition to load Win10 on, delete all previous partitions except for System and MSR if reusing a boot drive.  Then click on Next or Install.  Win10 will then automatically create the appropriate partitions and load.  If a window pops up asking for product key, click on link that says "I do not have a product key."  Win10 will then continue to install using the product key that's imbedded in BIOS.  You'll still need to activate it online.

If that doesn't work, something else is wrong.  Did you troubleshoot the HDD as suggested?  Did you test or replace the battery?

Make sure BIOS is set to AHCI and Secure Boot on.