Assuming that everthing is going to work fine, i will be able to connect more than one device to the router (or the access point connected to the rotuer) and use the encrypted connection on all the devices simultaneously?
You will be able to connect more than one device to the LAN side of the router and use the L2TP connection for all of them if the router itself would have a public IP address. All you'll have to do would be to apply src-nat (well, maybe a masquerade) on packets routed out via the l2tp interface, just as if it was a normal WAN interface.
If the router wouldn't have a public IP address itself, you may get in conflict with some other L2TP/IPsec client accessing the VPN service from behind the same publc address like your router. In that case, you would need to do a dirty trick on the Mikrotik to resolve that. If that is the case, come back for the details.
Instead of writing novels, post /export hide-sensitive. Use find&replace in your favourite text editor to systematically replace all occurrences of each public IP address potentially identifying you by a distinctive pattern such as my.public.ip.1.