You need to use den/det when you have an adjective (same for the green house: det grønt huset; the twelfth beer: den tolvte ølen).
I'm not a hundred percent sure you can say the first thing, but it doesn't sound very strange.
Also, just a little correction: it should be 'å bruke' instead of 'å bruker' in the last sentence.
This is definitely one of the essential sentences you need know how to say if you are going to Norway. ;)
Realistically though, unless you're a millionaire you're only going to say that when you go down to Denmark for the cheap booze because in Norway, beer (just like everything else) is really frickin expensive, also at most parties you're expected to bring your own drinks because the host would go bankrupt if he had to buy multiple beers for the guests.
Yes. When you talk about a measure or unit of beer, be it a bottle, glass or mug, it's masculine, while when you talk about different types of beer, it's neuter. You can talk about "et mørkt øl" but you usually buy "en øl". If you say that you want to buy "et øl", it would usually be understood, but an especially quarrelsome or pedantic bartender might then ask you how many you want of that specific beer.