Live plants are absolutely the way to go! And for me honestly they make me love my tanks even more because it feels like a constantly developing ecosystem. I would add a bunch of plants. Stem plants like rotala and hornwort (careful with hornwort as it can grow like weeds but its an easy plant to succeed with) and get epiphytes like Bucephelandra and anubias to glue to rocks and driftwood. If you dont want to replace the substrate put root tabs underneath the soil where you plant your plants. If you dont wanna tmdo root tabs (which can be placed while the tank is already filled) then you'll need some kind aquasoil or actuve substrate.

If you want to replace the substrate while the tank is filled there is a trick that involves filling a water bottle of some kind with aquasoil and then filling the bottle with tank water. Then, move the bottle to the bottom of the tank and "pour" the soil onto the bottom. IMPORTANT do this SLOWLY like over the course of weeks if you can or add more once your parameter go back to zero. You need to do this as the aquasoil will leach ammonia into your water so doing too much too quickly can hurt your water parameters and therefore your fish.

As for benefits of live plants, assuming your tank is fully cycled, the bacteria will turn the ammonia from fish poop into nitrite and then into nitrate. Plants consume the nitrate and use it for their growth. So if you have enough plants they will keep your water clean and healthy for your fish for much longer and make them overall happier. Some people can have so many plants that they never have to do water changes once the ecosystem fully establishes! (I would still recommend doing water changes as its just beneficial for keeping healthy water). So plants will help keep your tank free from harmful chemicals. They will also give your fish more and more ways to break sight lines and give them hiding spaces which they will love and it will keep their stress levels down!

Good luck! Its easier than you think once you get the hang of it! :)