Add substrate on top of Rocks or Gravel?

I have inert gravel in my tank and few plants I got like anacharis and hornwort are doing great. I want to add more plants that need nutrient rich substrate like carpeting plants. My LFS has Tetra Complete substrate which I can put first in the tank at the bottom and cover it with my existing gravel. However it is expensive and I can get only 1 bucket which will be fine for my plants.

I want to create an aquascape with slopes, etc so I need more substrate for that.

1) Can I add some inert gravel at the bottom or a layer of small rocks or cheap sand and create the aquascape? After that I can put Tetra Complete substrate and cover that with my old gravel. This way most of the aquascaping would be done with cheap gravel or rocks which would be covered with about 3cm of tetra complete substrate and 2cm of old gravel.

2) Will this have any negative effect on the plants?
3) If I leave my old gravel in the water whole time while doing this stuff, will the beneficial bacteria survive? If I leave my existing gravel there at the bottom rather than remove it. Then cover it with tetra complete substrate and add new gravel on top. Will beneficial bacteria from my existing gravel still survive and transfer to newly added gravel?

My tank is cycled, that is why I am concerned about gravel change.

 

Giving this a bump up for you hope you get some responses today

 

Bump

 

1) yes. Put the sand first then whatever u want on top of it. I think rocks are a little more expensive
2) I don't think it will
3)if the gravel stays in the water and you the bacteria will survive but it might take time for the bacteria to spread

 

jz1300 Thank you.