I also looked for advise when I was getting my first flowerhorn and then the Asian Aro. A lot of people recommended tank sizes way out of my reach and they are all overkill.
I completely understand the idea that you want to have your fish to grow to its maximum potential and size but think about it, this is a hobby. You want to have fun with your fish and you don’t want to be its slave for its entire life. Imagine doing 25% water change per week and monthly maintenance on a 300G tank. That’s a lot of work to do.
The smaller the tank, the less work that you have to do. I don’t have Silver Aro, but my Asian Aro is 18” and he’s happy with his 60x24x16” tank. He has 7 parrot tank mates. Tank is cycled so Ammo and Nitrite are both 0, Nitrates don’t do much. Weekly water change is still insane since I don’t add tap water straight to the tank. I just can’t imagine doing water change on a 180G tank, let’s alone 300G.
IMO, 6x2x2ft tank (180Gal) or even 6x2x1.5ft is big enough for Silver Aro. Remember, Aro just need the swimming space. They don’t dive a lot. I believe that shallow tanks are better for Silver Aro since they tend to develop drop eyes. Shallow tanks will help in that regard since the fish don’t have to look down much; however, drop eyes are from the genes but shallow tanks will help to some degree. Filtration is very important. IMO, Filtration is the one that you want to overkill, not the tank size. Bare bottom is the best since weekly maintenance includes vacuuming the bottom. You don’t want to go spot by spot on a big tank if you have gravels or rocks on the bottom. Sand will be fine. Some tank decors will be fine.
Just get the fish a reasonably big tank which you think you are able to do maintenance on it weekly and monthly. Know your limit. Don’t push it. There’s nothing wrong with asking but over the year, I learn that when it comes to tank sizes, people always recommend tank sizes bigger than what you really need and sometimes, it’s overkill. Just cycle the tank, put the fish in and enjoy.