P: Field "File Size in MB" should be available as a filter in Organizer

Not quite.  Pixel Resolution is not the same as PPI (scaling.)  Pixel count is the actualy resolution of the image.  The file size is impacted by compression and color depth.  When you change PPI you DO NOT change pixel resolution unless you resample the pixels/file.  A 2000 pixel image at 100dpi will print with the same resolution (quality) as a 1000 pixel image at 200ppi.  Basically, PPI changes your ruler.  I work with National print labs.  The 300ppi lab requirement is twice what most photo printers actually print at.  Then you're faced with limitations of DPI when you're printing.

I want to know which images have crops or are excessively large in my catalog for archiving and file management purposes.  I also want to know which images are small, have large crops, and might need super resolution.

Cheers!

PPI number alone has absolutely no effect on the file size on the disk or the pixel count. Easy enough to check. In Photoshop open any image, go to Image and Size, uncheck Resample, and change the PPI value to whatever you want. The file size or pixel count will not change. What would change file size and pixel count is resampling (upsampling) if you increase the pixel numbers for width and height. PPI is just an instruction for the output device driver (monitor, printer, whatever) but it does nothing to the pixel data on the computer. You may want to match the file PPI to the size of the print (for example) so driver or raster processor doesn't mess with it but there is no guarantee it won't anyway.

What affects image size greatly are non-vector masks and layers containing bitmapped data. In complex edits with many layers they can make the file size on the disk several to tens of times the pixel dimension size so in these cases pixel count is not very helpful. Then there is the file compression too. We need file size on the disk. 

I left Google Photos because it didn't allow for subfolders. Now I will leave Lightroom because I can't sort by size. Plain stupid.

I absolutely agree tha LR shold have this possibility. I am not a geek and using different apps is time consuming.

So, the "implementation" problem here is that these goodies aren't saved in the LR catalog, the lrcat file, which is in fact just an SQLite database, in a readily accessible format.

Each image/file has in that dabase -- obviously? -- an entry with its Adobe Camera Raw settings saved. However, very few of those parameters are stored in a way that allows them to be searched efficiently. Generally, the ACR settings are a text blob. Some of them are broken out into additional tables and indices, but not many of them.

Lightroom's ACR settings aren't (I think?) stored as JSON, rather as some kind of nearly-JSON but "string," and the relatively recent enhancements to SQLite for JSON queries probably don't apply. Oh, if only they did.

It wouldn't be much of a stretch for users to be able to filter on, say, images with Texture < -25, but it seems to me (naively and perhaps incorrectly) that the schema used by LR is basically REALLY OLD.

By the way, SQLite is one of the coolest things ever to be released upon the world, and if you are an SQL-curious nerd who hasn't heard about it, you should check it out. It has uses, and is used in ways, you would never expect.

Get AnyFilter as @johnrellis stated above.  It has filter capabilities that will NEVER be provided by Adobe.  

Lightroom needs this. I absolutely agree.

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The Any Filter plugin can filter by file size:

You can create smart collections for Long Edge

I have also had the need to search for cropped dimensions (with RAW or even bit depth) which would also help.  Even "longest" edge would help as I use that for exporting settings.  I was specifically running image enhancement on older images.