If I were you, and I would do a major water change. Avoid messing up the substrate. Drain the water down to the substrate, then refill with straight tap water but use a bowl so the water runs into that and slowly over the sides, as this avoids stirring up the substrate. If the cloudiness is partly or totally due to the substrate material, this should avoid severe cloudiness. This might also be due to a bacterial bloom.
When the plants arrive, if you have any that will be rooted in the substrate, drain the tank about half way, and plant it. Arrange the decor. When you have this done, then drain the tank down to the substrate and refill with tap water, again using a bowl to avoid stirring things up. The planting obviously will do this, hence the full drain/refill when finished. Connect heater and filter (have the tap water at the desired temperature to avoid over-using the heater which can cause them to fail).
The cloudiness should be less with all the above, but still likely, especially a bacterial bloom. Leave things alone and once the plants are showing signs of growth, you will be able to add the Betta. There is no other "cycling" needed.
