why are you stuck on mares for back inflate?
The back inflates still have huge disadvantages over backplates in wings in that they aren't modular and will not grow with you.
The regs have had quite a few comments but regulators are regulators. They all work, it just depends on how much you want to pay for them and pay to keep them. The cheapest you can get any of the Mares regs is $500 for first and two seconds. That's a yoke Prestige 12s and MV octopus. For $480 you can get a set of HOG regs, matching seconds *very important if you ever decide to get into technical diving*, full braided hoses, and an SPG. Now add the fact that parts kits are only $60 and you can learn to service them yourself, you can save a lot of money over the life of the regs. No idea what Mares parts kits are, but that is a huge turn off for most of us who save well over $100/year by servicing our own regs.
There's sitting on the surface no effort to lay somewhat back in a transpac, DiveRite classic wing, mostly full with LP72 doubles. If you have weight in the front, it will pull you forward, but if you have steel tanks or a SS backplate *not sure how much weight you had in your training dives, but a SS backplate and wing can take up to 10lbs off of your waist belt and with a comfort harness you are still in the price range of the Mares, just not from your LDS likely. $480 if you don't want a backpad which if you're in a wetsuit you don't need, $530 with one.
Computers:
Best computer on the market hands down is the Shearwater Research Petrel. Unfortunately it is also $850, but it's the last computer you'll ever need.
My criteria in a dive computer. User changeable batteries that are easy to find, and easy connection to a computer so I can download my dive log.
The other two options for that are the Nitek Q and the XDeep Black BT, both of which are right around $600. Those are above your budget since we're at $1010 for the regs and bp/w listed above.
Next best option now becomes the Hollis DG03 for $250
https://www.divegearexpress.com/computers/dg03.shtml
This does actually allow air integration should you decide you want that down the road, just have to buy a transmitter, I don't like them, but some do. It will run in Gauge Mode which is important if you get into technical diving and want a backup computer. Downfall is it doesn't integrate with your computer to download dive logs, and it does use one of the coin style batteries, but they last quite a while, so it's not that big of a deal. Would highly recommend swapping the watch strap for the bungee mount for $20, but it's optional.
Your total now is $1280 which is a bit more than your proposed budget of $1200, but you can cut $100 out of that if you don't go with braided hoses, the backpad, and the bungee mount. You have to buy from two different companies and not your LDS, but you save on sales tax, they both ship for free I believe, and if you wait on the regs and BC until Black Friday, you'll save a couple hundred more.
What I have listed above is by far the best bang for buck system that new divers should seriously consider before buying any other gear on the market. The $1280 price includes $100 for the upgraded harness, $25 for upgrade to braided hoses, $50 backpad, and $20 bungee mount, so you could feasibly be in for under $1100 for a full set of gear, that will hold it's value better than typical recreational gear, is easily serviced by the diver, and is all quality equipment that can be used for the rest of your diving career no matter if you stay diving 30' reefs, or go to technical cave diving *only thing you'd have to change is to a doubles wing and add an extra first stage*
