Area-51m R2, maximum storage capacity?

Hi @Nessman531 welcome to this free user-to-user Alienware laptop discussion forum. 

Alienware Area-51m R2 with interposer Sled boardAlienware Area-51m R2 plus NVMe Sled board

Dell expects users to remove the rear panel and this does not invalidate the Dell warranty. Dell provides Alienware Area-51m R2 and Knowledge Base Article support documentation. YouTube has Dell Support and Alienware Support information and videos. 

Support for Alienware Area-51m R2 Service Manual says there are four M.2 slots: SSD-1 and SSD-2 are on the motherboard, and SSD-3 and SSD-4 are on the NVMe interposer Sled board. 

To get these interposer parts, call Dell Support and ask them to raise an order for all the 20 separate parts (no url, no kit) which includes the 2.5 inch cage NVMe silicone interposer board D3P25, cable #1 2JH8P, cable #2 5F1WR and all the other separate parts of screws, etc. Also ask for all of these parts be included in your Dell System Warranty. (Interposer kit of parts is also available on internet.) 

The Crucial System Advisor database includes Alienware Area-51m R2 | Memory RAM & SSD Upgrades | Crucial.com. 

You may use a 4 TB M.2 2280 drive. You may also use the second drive connector in your laptop to add another M.2 as storage if you desire, if that connector is provided. If you didn't order the laptop with two M.2 drives, then you'd need to buy the bracket and heat sink separately.

According to the specifications, some options of your laptop model support up to four M.2 drives. That may depend upon other options.

Whenever touching components or working inside a computer, wear a grounded wrist strap, also called anti-static wrist strap, ESD wrist strap, or ground bracelet. It's a cheap and sensible precaution. Rest the laptop on an anti-static mat or at least a reasonable alternative such as corrugated cardboard.

Here's the full detail of what the specifications say for your laptop (but note that you can exceed the sizes listed, as you can go up to 4 TB each):

Storage

This section lists the storage options on your Alienware Area-51m R2.