Good that you are planning..The width might still be an issue.. 30" is like 2.5'.. aros grow to be 3ft+ and TSN will def get bigger.. you might need an indoor pond or pool..
As long as you don't add anymore fish, i think it should be ok.. really i think best is a large pool.. but yes given space constraints i understand.. just give it some more time.. lets see what the others have to say..
IMO a 96x30x24"(LxWxH) would be minumum for a single silver. Though if you want a community go wider and taller. Many people say that height is not important, but when you consider decor and the need for multiple levels of swimming it is important.
I think you will eventually need another upgrade to something that has at least 4' of width for the TSN. The cat will get to 40"+. To have it in a tank that is only 30" wide means it will have a tough time even turning around in the tank. I agree with Kaya, these large cats are better suited to ponds, not aquariums. The aros can turn on a dime, so they fair a little better in smaller tanks, but like Brian side, 30" is probably the bare minimum for one Silver aro.