Best way to share a network drive in windows over the internet and how to do it?

You are going to have a bad time if you try and stream video directly from a shared folder over the internet. You would want something like Plex server serving the content, and even that will be very dependant on your upload speed. 5Mb/s is not going to cut it, and if you saturate your outbound connection your internet will slow down to a crawl for anything else on the network.

And don't publicly expose anything to the internet. Setup a VPN and tunnel directly to whatever resource you're trying to access on the LAN.
If it is a general use PC, then bad idea. If this is the only reason for it to exist, then get a real firewall, stick this PC in the DMZ, limit the connections to only those needed for the share, and accept that you will likely have to scrape and reload every so often. Bonus if you get a firewall that supports VPNs native. Then you can block all access to the PC except via the VPN.