Sounds fishy as 12 Gpu do not run well or do not run at all with only 4GB of Ram. There is the common consensus between small home miners that up to 8 cards can run with 4GB of Ram although not recommended, the usual recommended Ram is 8 GB if you are mining with a device which has more than 8 cards.

After searching the website of dominorig I don't see office location so anyone interested can go there and check by themself and also the website is done in a very cheap and unprofessional way with Wordpress. These are big red flags for me so I would be cautious to say the least.

which OS is installed and what mining software comes as default?

Can't speak to the price, as we use exclusively Nvidia these days but I've used a bunch of these Chinese cases - they're all much better than open frame rigs IMO, as you can control airflow, and most are using riser-less motherboards, which is a must have for me.  If you're home mining, then open frame rigs are great - not saying you can't industrial mine with them, they just are much more work in my experience.

Some cases are better designed than others, and for my purposes their G12 isn't the best - in particular how they have airflow setup.  I suspect they didn't spend any time modeling airflow, and just tossed vents and fans all over it - by this I mean they have vents on the front that are far too close to the intakes, so if there is any kind of positive pressure inside the case, it's going to short-circuit the airflow and suck in hot air from the case.  Then it has two kind of random fans stuck on the back top, which makes these cases unstackable and I have no idea what they thought they were doing with them, as it disrupts the straight flow of air you want from the front right out the back.  Venting on the back is a bit more of a mixed bag depending on what they're doing - the open area around the connectors I personally like, because it tends to help the airflow around the PSU, which has a tendency to trap air around it and get hotter than normal.  I also like the extra-wide card slots, as once again it helps keep the air flowing inbetween the cards, instead of just over them, like the slots across the back top do.  All in all not the best design - solid meh from me.

My preferred cases are these:

https://www.ebay.com/itm/Awesome-6-GPU-Altcoin-Mining-Rig-Case-just-add-cards-Fast-US-Shipping/253663963171?hash=item3b0f8ce823%3Ag%3ACsQAAOSwl5VbBcA0&_sop=16&_pgn=3&_sacat=0&_nkw=gpu+mining+rig&_from=R40&rt=nc

Although I've used these with success as well, although I prefer the PSU on the other one as it's a more tradition ATX:

https://www.ebay.com/itm/8-GPU-Mining-Server-Case-w-4-FANS-Motherboard-Power-Memory-Rsiers-Frame-Rig-ETH/401486164608?epid=27014163342&hash=item5d7a70b280%3Ag%3AhaIAAOSwcSxacuOV&_sop=16&_pgn=3&_sacat=0&_nkw=gpu+mining+rig&_from=R40&rt=nc

Generally on these cases you'll see vents on the sides or top, but they are more to normalize pressure in case (to extend fan life) than for anything else - although they do disrupt airflow a bit.

Also keep in mind that any of these machines PSU really isn't going to work well at 110v - I'm not saying they WON'T work, just that they won't work for long.  

One more somewhat random comment - as I was searching on eBay for cases, I ran across this:

https://www.ebay.com/itm/MINING-RIG-GPU-SYSTEM-MP1061009N-9xGPUs-6GB-225MH-s-ETH/142870841634?hash=item2143c40922%3Ag%3AJzcAAOSw2khbTTpZ&_sop=16&_pgn=3&_sacat=0&_nkw=gpu+mining+rig&_from=R40&rt=nc

Before you get excited it's a scam, in particular the fact it says 'PLEASE NOTE: Delivery ~ 30 days', so just be careful - I've run into that lately on eBay, they try to get outside of the 30 days easy return period the eBay normally provides.  It never works, but it can tie up your money and be a huge PIA.  I also wouldn't buy from random places you find on Google - unless it's a provider that's been around for a while, just stick to eBay or the forum (with escrow), and you'll probably have a good experience.

Either way, Good luck!

Price wise is reasonable

and power consumption for 12 GPU + cpu system at 1600w is also a plus

however, risk is high, not sure how they treat warranties

I was just overthinking the way bitmain handles horrible warranty claims

I have a 13 RX580 rig with 402 mh/s and 1750W draw on the wall. Hence power consumption is possible. But max hashrate to squeeze out of one RX580 maybe 32 mh/s x 12 = 384 mh/s.