Come on, mister, if you want to grow plants, get some plants in the tank!
Fill up all that empty space with a keen growing plant, perhaps Hygrophilia polsperma? Keep whacking in the ferts at at least the recommended doses, make sure you've got plenty of co2, change 50% of the water per week, and watch the plants. If there is a centimetre or more between the pairs of leaves on the HS increase co2 and fertilisers. When these plants are growing well, start to worry about more demanding plants.
Have you been told or read that large areas if your tank should have no plants in them? I'd love to hear where!
Re read the advice you've been sent, get some cheap hardy plants, fill your tank with them, watch them and learn from them!!
Wishing you all the best! Please let me know if anything I said was unclear/you have any questions.
Mark