I am pretty sure Abysmal is Joel Silverstein's company (who frequents this board). I haven't seen much of the gear, but I would imagine that the wing will fit any standard 11" on center backplate. Once you set up your harness on the BP, you can use it for singles or doubles. That wing is probably too big for any doubles diving you would want to do and is definitely too big for singles. So you can use the BP/harness but you will prob need another wing for singles. You really do not need a lumbar pad, but if you have your heart set on one, Dive Rite has one, OMS has one, Halcyon has one, and I believe Oxycheq does as well. Usually the pads and accesories will only fit that brand's plates (they use the accessory moutning holes as opposed to the standard webbing and bolt holes).
As for the regs, You will be better off with a dedicated set for singles and a dedicated set for doubles. You will tire of switching hoses back and forth very quickly. However, as a new diver you probably will be safe sticking with singles for a while before you have the need to dive doubles. Like I said, ping Joel about details on the reg. You can look him up here or check out Tech Diving Limited. If I remember correctly, they were sourced from scubamax, or one of the other reg OEM's. They should be fine for what you need.