Sorry for the long post. I am just throwing ideas at you. Pick of it what suits you.
Seeing on the pictures that you may have a window in there? Position the plants right where the window is so they get natural light as well as artificial. If you decide to get LED floodlights, get the ones that are rated 6000K. There are thinner/slicker versions available out there.
The more light, the better as these plants use atmospheric CO2, meaning their growth will only be limited to the nutrients they get from the tank., given sufficient light intensity, not just duration. A pond with big monsters should naturally produce enough nutrient, hence the benefit of plants.
In my small pond, which is not that heavily stocked, I run out out of nitrogen and if I take a closer picture of the back of the plants, they show nutrient deficiencies(older plant leaves yellowing) all the time. This is good, as you know the plants are doing their job mopping unwanted nitrogen from the water but at any one time there should be enough for the plants to grow well and be overall healthy. So dosing nitrate and potassium for example is not out of the question if you want really healthy looking plants. Micro-nutrients are normally sufficient from water changes only, and if your tap water is on the hard side, so is calcium and magnesium.
Having said that, I don't dose and judge by the overall health of the plants. I do have nutrients on hand to dose if I wanted to. The plants are nutrient deficient enough to know I have enough plant mass/do enough water changes to keep the water low on nitrogen, but also there's enough nutrients to keep the plants going. Macro nutrient deficiencies, as in nitrogen deficiency, generally manifest in older plant leaves yellowing/dying. Micro deficiencies manifest in young/new leaves not developing properly. That's how you know what the problem is.
Recently I put two more plants, for aesthetics, not for efficiency this time.
I also use a TDS meter(which in fact measures conductivity). If the TDS increases gradually over time, not enough water changes are done. The TDS in the tank should always be in line with the TDS of the source water. This way you know your maintenance level is sufficient.
This method of monitoring water quality has worked well for me for years. I have 6-7 years old fish in that pond that have never been sick. They lived in a similar set up previously, with emersed plants. I have not measured nitrates in about 4 years, only use a TDS meter , not just because its faster and cheaper but because nitrates in a tank with plenty of plant mass that use atmospheric CO2 ,and lots of light, are always very low/deficient(once the plants establish), but TDS detect all other buildup, not just nitrates. TDS will still keep increasing d Some people are of the idea nitrates are the only evil, which is not the case....
Plants can take up anything from 1 to 3 months to really establish with their roots in water, but once they do, they'll start growing rapidly. I have pictures somewhere of my peace lilies flowering beautifully in my previous tank. The parlour palm hasn't stopped flowering for months but its flowers are not as nice as the peace liliy. It has flowers on the picture but you can't see as they look like a green branch with tiny yellow flowers.
If you get a parlour palm(which I strongly recommend as they are beautiful and hardy), keep in mind it is a very slow grower. Mine is about 5 years old. It is now big and bigger in person to see but it took years. So you may want to plant more plants/in number at the start to get sufficient plant mass. The peace lilies grow way faster.
Also, another interesting fact you may not know is that many of these plants, including the ones I have, have the ability to kill/inhibit mould around. As humid the room is where the tank is placed, there's no mould at all...And I live in a very humid/cold country, mould has always been an issue in all places I lived. In fact, there's mould in my bedroom that developed over the winter, but not in the room with the tank
Good luck. I am really looking forward to see your pond develop. For me converting into round pond set up was the best I ever did. I've never seen my fish as happy, outgoing, relaxed and friendly.