I was informed that it had 2 3.5" HDD bays, so if you purchased a SSD I am guessing its a 2.5" form factor. You should be able to get a 3.5 caddy to go with it. Just ordered this too, what is your order status? Mine shows up as estimated delivery in July!! 

I'm going back and forth with them because I paid for the Rev 9 last Friday, and the evening of Friday I noticed Rev 11 came out. I immediately told them to switch to the new Rev 11. But I was pushing them to give to me with Windows 10 Pro, not Home edition since I'm using it for work also. So don't know when my shipping date will be.

Good luck with yours.

PCWorld has Win 10 Pro for $39.99 through the end of June 2020.  See https://www.pcworld.com/article/3562330/exclusive-deal-get-windows-10-pro-for-39-99-thats-80-off-retail.html 

So you could buy the Win 10 Home and pay $39.99 for a Pro key if you don't want to wait.

I recently took delivery of an R10 with the 2tb ssd.  I also, like you ordered a 4tb SSD from Amazon (Sammy 860evo) and installed it in the 3.5" bay using this adapter from Sabrent;

https://www.sabrent.com/product/BK-PCBS/2-5-ssd-sata-hard-drive-desktop-3-5-sata-bay-converter-mounting-kit/

FWIW, the supplied 2TB drive in mine is a Kioxia.

The 2tb isn't a drive size limit, it's just the largest Dell validated drive sold stock with the system.  Dell only tests the system with oem drives sold by Dell.  Doesn't mean retail drives (bigger or smaller than 2tb) won't work.  

For a boot drive, a 2tb limit only impacts you if you format the drive with the mbr file system (used with legacy bios). 

According to the manual, it's limited to 2TB per 2.5 and 3.5 in slot. Is that not the case? Have you successfully used a 4TB drive in these slots?

I have an A51 R2 it’s got 2x ssd, 3x HD’s.   If u connect any drive (ssd/HD’s) to HD’s cable, (serial 3-5) u have the option in boot to create a raid volume / format that is combination of the size of at least 2 drives.

   So, a delivered r11  with 2tb m2 and 7209 rpm 2 tv drive will have the 2 empty ssd trays—-  is r 11 same as storage controller and allow the volume as total space of each??++?

This is just a futureproofing note for anyone who is going to purchase this computer and does not have it configured yet. I used to be into modding and I am familiar with installing motherboards, etc.

Just so you know the inside of this computer is fairly business computery while the outside is awesome. The inside is completely vanilla which is fine with me.

I bring this up because I ended up buying two of these computers. On one I have the 2 TB SSD C Drive, and then I had Dell install a 2TB 2.5 HDD and a 2TB 3.5 HDD. Then I swapped out the 2.5 for a 4TB SSD and swapped out the 3.5 for a 14TB HDD.

When I got the other machine I only ordered a 3.5 2TB HDD extra. The problem is that when it came the extra unused 2.5 slot was kind of full of wiring, connections, etc. It would not have been hard to rewire it but I was not up to it so it just has a total of 2 drives.

Comment for people who are going to order this computer: If you think that you might want to use all the hard drive slots down the road then go ahead and order an inexpensive drive for each slot. That way it is extremely easy to swap out the cheapo drive with the drive that you decide to install in the future.