Adding Soil To Fishtank

The first thing to say is that some soils leach ammonia into the water for up to 6 months, and fish can't be put in the tank till it stops. I don't know which brand of soil you are thinking of, but I suggest you do a search to see if yours has a reputation for this.

A food safe storage box is fine for the fish, but ideally big enough to hold the filter and heater. Can you get all the media into the smaller filter?
Bacteria can live a fair while as long as the media is even just damp and floated in water so it's next to air for oxygen.
It's less stressful for the inhabitants than leaving them in the tank while you do it, but still stressful. Leave the lights off for the rest of the day, and maybe even the day after.
If you will be putting the same water back, it'll just be like a large water change. Provided your routine is weekly water changes the tank water should be fairly close to tap water anyway. The real need for acclimatisation is when the fish are moved from a tank with completely different water or if tank maintenance is poor where the tank water has been allowed to become different from tap water.

There is a chance of a mini cycle. To minimise the risk, don't feed the fish the day before or for a couple of days afterwards. Then feed less than usual for the next week. Less food = less ammonia.

Thanks sue I wasn't aware of soils leaching ammonia. I was going to use dennerle nutra basis 6 in 1 but I now have to rethink. The filter would never fit all the juwel sponges so I would have to float them like you said.i will do as you said about feeding the fish.@ Matt I can move all the plants but would have to float them as I'm not sure how could anchor them down without moving. I do have 2 large driftwood one with java fern on and one with moss. If I added extra rocks to the main tank now would that hold a lot more bacteria by say June and help the cause.

One more question if I tried to scape the tank with new plants and wood,would this work or do i have to use all of the previous wood and plants ?

Thank's again sue I will float the sponges and I think
I may have some soil left over from the shrimp tank I can test.

Thank you Matt & Sue this opens up a lot more options for me now. @ Matt i was thinking of adding Myriophyllum mattogrossense (Green) or Elodea densa or even water sprite as the fast growers.

I was planning on trying to run some kind of filter, but the only problem is i don't really want to cut the sponges to fit the the filter. I need to look around to see if i can find a cheap filter that i can squeeze at least one sponge into and then float the others.