It's tough to light a tank with one spotlight and it's tough to flow a tank with one powerhead.
And at 48" you're kinda at the limits even for what Kessil recommends for that light.
But if you're OK for now (a light meter will help you to know for sure, lux or PAR – don't guess!), later on if you do end up with "issues" I'd look at supplementing with an additional A360W.
Switching to three A360W's wold be a similar strategy if you'd be worries about the asymmetric look over the tank...but they'll all blend well together no matter what combo.
If you really feel more drawn to adding T5's then I'd suggest maybe swapping the Kessils for some comparable LED strips.
Strips, or "bars", will put out light that is
a lot more like T5 than the spotlights you have now. GHL, Current, Hamilton Technology, and several others make good strips.
And I know you were half kidding about being "lucky enough", but just to throw it out there:
Big colonies take patience an planning. Luck, even when you get it, always runs out! If you take your time and do it right, you really won't have problems.
