
Photo showing about 90% of the aquarium.
Hi folks, I'm looking for a little advice.
I'm completely new to this and this is our first aquarium which is now a few weeks old (photo taken after 2 weeks).
I let my mother and my daughter set up the planting, basically because my mum is a landscape gardener and is good at that sort of thing, and my daughter wanted to choose the plants. I took the view that the whole family could get involved, and we would suck-it-and-see as to what happens.
I think it looks okay for a freshly planted tank, but it was done with no regard to the type of advice given here... and all the labels for the plants got thrown away so I have no idea what any of them are.
But I'm so please with it, I'd like to take things further and would like some advice as to where to go next?
Here is where we are so far

It's a Jewel Rekord 120 with standard lighting. Substrate is black gravel only. Decor is grey slate and burnt wood.
I'm in a hard water area, pH is 7.2 (I'm told by lfs after they tested my water). Amonia and nitrite are okay, although I have just had what appears to be a mini cycle which I believe may be cause by some of the plants decaying. Nitrate is surprisingly low at about 20 -- I have the standard Jewel filters including carbon and nitrate sponge.
I'm using a weekly liquid fertilizer - API leafzone.
The foreground plants started to yellow and decay. I have removed them to a makeshift tank in the garden where I hope they will get plenty of light in this mini heatwave. I have ordered Interpet single T5 compact 36w lighting to compliment the Jewel standard 30w T8 -- although there seems to be a problem with the order and it's on hold. So I could cancel this and get something else if anybody has a better idea? I don't want to spend a fortune because I'm cleaned out after buying the tank, and I plan to upgrade in a more serious fashion at a later date. I shall also add an external filter when my finances are replenished.
The foreground plants were planted properly between rocks, but the other plants are still in their pots which are just buried in the gravel.
Do you think it best if I remove them from the pots and plant them with some laterite mixed around the roots? Or maybe kitty litter, or should I just use tabs? Am I going to need CO2?
I have been having some problems getting additional plants from my local stores. They have plenty but not much variety. Ideally I'd like to double the number of plants.
Many thanks in advance.

P.S. I think one of the plants is a house plant (centre left)