How to make a file server through a router with access from the "outside"?

Question

Computer networks

Good day everyone.
The thought came to my site to tie an external usb hard drive through a router to my site.
Since the place in the cloud is obscenely expensive, and plus 1-2 TB is almost free (considering that you already have a USB hard drive).
So, the site is located on a regular hosting, with the usual domain name mysite.ru.
Question 1st. How do I set up file storage?
There are 2 routers at home.
The first from Rostelecom, optical fiber. Model NTU-RG-1402G-W .
After some digging on the Internet, I found out that it fully supports USB hard drives, but you can access them only via FTP, which is not very convenient. But even so, I can only access it from the local network. From the external Internet, access cannot be configured yet.
The second Zyxel Keenetic 4G III router works as a repeater (amplifier) ​​of the first wifi signal, but this mode can be abandoned. However, officially this router does not support USB hard drives, only USB modems, but again, you can get confused and install unofficial firmware that connects hard drives through crutches.
Question 2nd. How can I make it so that when I enter a link, for example mysite.ru/download/file.exewas the file downloaded from my USB hard drive? I suspect that this is the least of the problems and is solved by redirects, editing the .htaccess file, or something else.

Answer 1

reflash in openwrt and then work as in a normal server linux.
speeds depend on resources, and there are very few of them in the router, for ftp ssh, etc. file storage, without graphical interfaces, enough for the eyes.

Answer 2

For me, this is a huge garden that will cause pain, the file transfer speed will rest on the ability of the router chip. For the sake of such experiments, I would simply assemble a mini-PC and make a full-fledged Linux server on it, or even use a solution for a personal cloud