1) if so, no big deal. As long as it doesn't create a nuisance for you (sound, salt creep, etc) and gets water to the screen
2) I would say most definitely not enough light. The LED flood lights are at best enough for a 5x5 area, MAYBE 6x6, so you would want 4 of these on each side (one on each 'quadrant'). For DIY LED arrays, I recommend one 3W 660nm Deep Red LED on each side of every 8 sq in of screen, minimum. For your screen this equates to 16 LED or about 50W per side (watt in this case being the 'nameplate' rating of the LED, as a 3W 660nm LED does not necessarily consume 3 actual watts). For the eBay floods I tend to recommend on the conservative side, hence 4x 20W floods.
3) 10x13=130 sq in /12 = 11 cubes/day based on the feeding guidelines. I would scale it at maximum so that it is no larger than 2x the feeding guideline. So you would be wanting to feed 5-6 cubes/day for this size screen (if the light, flow and roughness were on par)
So you're in the right ballpark. If you revisit the sizing and scale back, you may be able to use less light and flow and still get the filtration you want. Especially if this is not your only source of filtration.