Help with final transition from saltwater to first palladium

[FireBellyValoo]

Hello!
I'm starting up my first palladium as well as a modded tank, while I've kept saltwater fish for quite some time, I'm new to keeping amphibians and freshwater, and I'd love some tips for improvement to my tank as I've got some slow days next week to work on DIY projects.

Tank Size: 20 Gallon Long (30in x ~12in x ~12in)
Water Gallonage: 12 Gallons

Intended Residents: 1 Firebelly Newt, 6 White Cloud Minnows, Java Fern, Anubias, Java Moss

Currently Planned Projects:

• Replace the tarp under the waterfall and ledge to climb up with thoroughly cleaned astroturf to better separate the land and water and to prevent soil from eroding during water changes (which is why the tank is so dirty right now, did now expect so much soil to be pulled away)
• Make an acrylic folding lid that fits the tank (has odd dimensions), and has room for all the cords and various doohickeys attached to the tank.
• Extend Sump Pump with 1/2in PVC so that it's not sucking from the top of the water

I'd love to hear any more ideas! In advance, I did pick any smaller gravel away that the newts may consume before placing it in the tank, and I can't go any larger in tank size since I'm still a college student and will likely have to move every year or two until I settle down (Apartments and dorms usually allow 20-gallon tanks, and I can pass it off as a 10 gallon).

 

[FireBellyValoo]

If the pictures didn't show up, here they are.

 

[Chinadog]

I would add lots of live aquatic plants for the firebelly, they are never happier than they're hanging out in the plants just below the surface. I would honestly ditch the gravel and go for a thin layre of sand. Gravel is very good at trapping waste and general dirt so it's a pain to keep clean and any live food you put in for the newt will quickly disappear out of reach into it.
I can't tell if that's a heater stuck to the back there? if it is it's not needed, the minnows are happy in cold water and the newt will really struggle in a tropical tank.
Good luck with it, looking forward to seeing it develop!