Love your enthusiasm and please try to keep it going!
I would highly recommend not trying to build your own tank, as too many things can go wrong.
You likely could accomplish your goal of staying below $2,000 but it is important to research twice and buy once. I cannot tell you how much money I have wasted on buying things twice when trying to cut costs.
Reccomend you check out
https://www.reef2reef.com/threads/the-supreme-guide-to-setting-up-a-saltwater-reef-aquarium.138750/ to get basic information on what you are looking for to set up a tank. the link will have all the information on equipment you need.
Just so you know, sumps typically go directly below the tank, housed within a stand, which will not affect your overall footprint, so you could keep that additonal space to the side open for an ATO or somehting else you inevitably need down the line.
I have had predator tanks and they are great, rays are one fish i have not had but they are very similar in terms of care to sharks. Need as much open substrate as possible, and look for a more softer, finer substrate so they dont irritate their bellys.
I know it is hard to do, trust me, but try to come up with a full plan on everything and then buy rather than try to do it piecemeal. You could even get lucky and snag a second hand tank or specific equipment on the cheap on CL or Facebook.
Keep asking questions and helpful people will answer you, you will never stop learning things on here!
