I've had my 6.8 bottle for about a year now. I'm very happy. They make a padded carrying bag for 20$ on aliexpress. I think it's nice and keeps the tank looking nice.
G5/8 is also known as DIN. Get a DIN 300 fill adaptor. There are hundreds of different brands and suppliers. Try eBay, Aliexpress or Amazon. You will find one for as little as 20 or 30 bucks with gauge, hose, bleed valve and foster fitting.