Paste on multiple layers at once?

You would need to use a custom script for this.

Im kinda baffled why most to all answers above are almost all about something completely different. I see stuff about opening documents. Is this forum getting totally mingled or what?!

Something like this which will open all files in a given directory, filtered by case-insensitive file extension... 

/*
https://community.adobe.com/t5/photoshop/opening-images-in-reverse-order/td-p/11294160
Opening images in reverse order
*/
var inputFolder = Folder.selectDialog("Please select the folder to open the images in reverse order:");
for (i = !(fileList = Folder(inputFolder).getFiles(/\.(jpg|jpeg|tif|tiff|bmp|png|eps|psd|psb|gif|tga)$/i).sort().reverse());
    i < fileList.length;)
    open(fileList[i++]);

https://prepression.blogspot.com/2017/11/downloading-and-installing-adobe-scripts.html

Using .reverse() will load the files such as:

003.psd

002.psd

001.psd

(003 at the first left tab, 002 in the middle, 001 on the right tab which should be the first doc open/visible).

One can remove the .reverse() after the .sort() if required for the opposite order.

I'm not sure how to call the open dialog for interactive manual selection of only certain files, perhaps somebody that knows can post the code.

A Script like load files into a stack  has an interactive files selection dialog where you cam select files from all over the place from many folder one many disk.  Once  you done with your selections the script start and creates a document withe layers containing the composite images of your selected files.

The point is such a script could open the files in any order you want if there is some logical order.   If the select you want to process is something simple  like all the  images in a folder or all the psd files in a folder the section process  would be as simpler select folder dialog.  The script  would get the list of file and open in the reverse order process the list from the end to the beginning.

Uh, sorry I missed the point, it is about open documents not layers.

Ctrl + Tab will select next tab as already explained while Ctrl + Shift + Tab selects previous tab. You can aso click on two arrows on the right side of tab list and to select first or any other open document.

Not sure what exactly you want but there are multiple ways to select bottom most image in the Layers stack without clicking on each layer separately. One way is using keyboard shortcut Alt + , (comma) while Alt + . (period) will select top most layer. You can scroll down and manually select bottom most layer, to record action to select bottom most layer or even to fully automate and instruct photoshop to play action on Open Document event https://www.designeasy.co/2018/06/how-to-automate-boring-tasks-using.html

I often use the keyboard shortcut (Command/Control + ~) to cycle through open files within Photoshop. The great thing is that when the last file is the active document, the keyboard shortcut will jump you to the first image.