1. Remove what you're calling adjuster thingys. They won't help you tension the chain as they're essentially just blocking the dropout where the are. I'm not sure if you could put them in front of the axle once you get the wheel in, but I'd expect it would do little above the actual axle nuts.

2. As per BBwimp, send back the kit. With dropouts as horizontal as you have, there's no need for a tensioner. Tensioners are for when you have inadequate dropout space (as in vertical drops) to adjust chain tension by moving the wheel back and forth. If you are using a cassette, you can get a sprocket and space kit or just the sprocket and use old spacers from a pooched cassette (which if you don't have you can get free or at a negligible cost from your local LBS).

3. Maybe.