Making my DS218Play work as web and mail server for my website

[Stardust]

Hey all.
I got a new ASUS RT-AX56U router with Merlin's 386.1_2 firmware.
And my Synology DS218Play NAS.
My webhotel provider almost doubled the prices last year..
So I plan to migrate my website to the NAS as I don't think it is worth the price anymore.

What I got already:
My own webdomain and paying directly to the national webdomain administrator (dk)
My own private external IP4 address.

What I need help for:
1:
Link to NAS through my router for both webserver and mailserver (both are installed)
2:
How to get a secure (https) server running, preferably without payment and simular regarding mail server.

If I need to explain better please ask

Thanks for any help (please if possible step-by-step)

Regards

John

 

[Stardust]

I got the web page up and running, but on port 80 and without SSL.
I also managed to run the web page from the external IP4 address.
So far so good

But: I still need help to make the site work with the necessary security.

Let's Encrypt, I understand it requires port 443 transferred to NAS. How do I do that in Merlin's 386.1?

What should I do to make the site secure - preferably for free?

Similarly with my POP3 / SMTP mail server. What do I do best?

Regards