As for what ports you need to forward on your NAS, it depends on what external access you want to have. Keep in mind that the more access you provide to your NAS, the greater the chance of some miscreant trying to hose it.
So, if you only want to have access to your NAS so that you can start a BitTorrent download from a remote location, then you only need to forward port 8080 to your NAS. No other ports need to opened/forwarded. Also, the BT service is NOT password protected, meaning that anyone that scans your public IP on port 8080 would have unconditional access to bugger around with your BT settings, etc.
If you want HTTPS access to your shares (and/or FrontView web administration), then you need to forward port 443 to your NAS. This will allow you to access any documents or files in your shares from a remote location just by using a web browser and going to https://your.public.ip.address/shares/ (or https://your.public.ip.address/admin/ for FrontView access).
Likewise for FTP. If you require access via FTP, forward port 21 to your NAS and then you should be able to access your files via FTP.
Keep in mind that these services must be enabled for each share (CIFS, AFP, FTP, HTTPS).
I hope this makes sense.