This could be a very long message without really providing you with an actual answer, so apologies in advance.
Real plants help water quality by using up the fish waste, etc. I also use floating plants in some tanks to lower my nitrates as they are 40ppm from the tap.
Live plants as a bit like fish, they will thrive in certain water conditions. Unfortunately this isn't always made clear at point of sale, but there has been a recent thread on this forum with a lot of information on this, so it may be a case of finding plants that work with your water conditions. Some plants also require a lot of maintenance (fertilisers, carbon, trimmimg), and others don't
I have quite a lot of different plants, and have made some awesome mistakes with them over the past year or so, and have not found a basic list of plants that work well with my water, and don't need too much looking after, which works for me as my focus is more on the fish than the aquascaping. By the way, my basic list doesn't have any stem plants as I forget to maintain them, they go stringy and lose their bottom leaves.
Another option, which
@Sue uses, and which I have used in my axolotl tank and river tank, are plants which can be attached to the decor. This will avoid your fish moving them, and the plants are (generally) slower growing and need less attention.
I have seen some awesome tanks that have no plants at all, and if you consider certain fish, this could be a very accurate representation of their natural environment.
As far as rocks go, anything that is from the garden would have to be cleaned and tested negar for suitability. This is off the top of my head, so I can't give accurate details, but if the rocks fizz with vinegar they are not suitable because they will release minerals into the water.
So, after a lot of ramble, it boils down to how you want your tanks to look. Lots of decor/limited or no plants can still give your fish a suitable and interesting environment. If you want plants but don't want to spend too much time looking after them, get the ones that are suitable for your water conditions and the way that your fish use the tank.
I hope that's of some use and has given you some things to consider.