I would use 9 Cree XP-G spaced 4 inches apart in one row across the top of the tank. That should give you about 40 micromols of PAR at 350 mAmps, 70 at 700 mAmps, and 90 at 1000 mAmps. This is with no optics. You don't need optics if you have the LEDs right near the top of the tank. And, without optics the light spread will cover the whole substrate very well. Use a dimmable LED driver, so you can adjust to whatever brightness you want.
If you mount the LEDs inside an aluminum channel, about 3 inches wide by 1 inch, with 1/8 inch thick walls, that should be a good enough heatsink, with no fans needed, and the walls of the channel will prevent the bright LEDs from bothering people in the room.