I'm not bashing your grow, these are just some suggestions, and you can take them or leave them as you desire:
Paint the inside flat white, not silver. flat white reflects light better, silver absorbs it. Or better yet, you can get a security blanket/space blanket (whatever they are called in your neck of the woods, it's one of those blankets that folds really tiny and is stored in first aid kits). Cut that to fit your box and use some spray adhesive to keep it in place.
Get your plants as close to the LEDs as possible. I keep CFLs 2-3 inches away from plants and don't get burn unless a leaf actually touches the bulb, I'm sure you can get your plants at least that close to LEDs.
I know you want low wattage grow, but think of this: 5x20watt floro tubes is the same as a 100w incadescent bulb. 2 grow boxes = 2 new reading lamps on your electric bill. I only say this because I have seen the results of quite a few LED grows on this, and other forums, and every plant I've seen has been majorly stretched and many haven't produced even as much as a cfl grow using the same wattage would have. It's an exciting technology for sure, and one day we may all be growing with it, but that day is not here yet.
With a COP (OMG! why are you growing?) right next door you will really have to control odors. Do a search for Carbon Scrubbers. They are very easy to make, it's pretty much taking a charcoal filter and making air flow thru that before it flows outside the box. If you control the air in your box, you also control the odor.
I would throw some red LEDs into your vegging box, and some blue LEDs into your flowering box if you still plan on using just LEDs. Just because a plant uses more blue when it's vegging doesn't mean that it doesn't need any red at all, and vice versa.
If you have a seedling that is falling over, take a length of clear plastic straw (size of the stem) and cut it length wise down one side. Open it up, and wrap it around the stem, then push the straw gently into the ground until the straw can prop up the plant on it's own. I've always used this trick for seedlings because it's much easier to put on and remove than tieing them to a stick.
That's all I can think of off the top of my head, I'll come back and post if I can think of anything else that you could use.
Oh! I did think of one thing! Miracle grow is horrible stuff! The soil I use is Black Gold. This comes in a variety of styles, most of which are nutrient free. They even have a coconut mix that is most excellent
And another! If you can't find a security blanket, or you want something better, go to your nearest party store and buy a couple of the big mylar balloons. Separate them at the seams and glue them to the sides of the box shiny side out. It sounds ghetto but mylar is one of the best things you can use for reflecting light, plus it would look sick with your LEDs
I wish you luck with your grow! Start a grow journal, I'll be sure to suscribe!