I breed these newts, so maybe I can help out.
Sand is perfect for newts - the small grains will pass right through them. I only use sand in my tanks (with root tabs for rooted plants). Eco Complete is probably not okay because the grains are large enough to cause impaction.
Don't really know much about installing filters. These newts really prefer still water. I use a very teeny filter (rated for 15 gallons or less) on my larger tanks or no filter at all.
Just some tips:
These guys really don't need a land area at all. If conditions are right (colder water, no strong currents, deep enough water, no fish, lots of plants) they will never leave the water. Just give them some plants that touch the surface, so they can rest at the top.
A secure lid is a must! They are very agile climbers and can squeeze through the smallest crack.
To encourage breeding you'll need to drop the temps (but if you're already seeing breeding behavior, maybe they've dipped enough). Females will lay on any 'floppy' leafed plant they can find. They fold each egg over in a leaf and glue it shut. This might ruin delicate plants like crypts. I keep some cheap plants in the tank during laying season: elodea, pennywort, water wisteria. They will eat the eggs, so you might also have to cut the leaves off to get them out of the tank.
From your pic it looks like the water level is really low - try to raise it to at least 6-7 inches deep. I keep mine in fully planted aquaria filled to about an inch or so below the top.
If you have any luck with egg laying, I can help with larva care too
but that's a lot to write at this point.