There are literally hundreds of Aquatic Plant Species commonly available. If you go to your local pet shop they should have a selection in stock.
No.
no. they live in mud.
Provided they will not leach sap into the water they should be OK. Otherwise the twigs/branches could poison the fish. Most smart people use live water plants as decore in their fish tanks.
they put them in their fish tanks and admire them
You can put some but not all cold water fish in tropical tanks for example you can put zebra danios and mountain minnows with tropical if you gradually increase the heat. You cannot do this with goldfish. It depends what fish you have.
No, you do not have to put real plants in a tropical tank, you can use fake plants if you like. Many people put live plants for aesthetics as the greenery tends to look very nice with small colourful fish
fake plants my fish loves them
Seriously, why would you want to? Is there something special about poison sumac?
the best plant would be a live one plastic plants can cut or damage the fin of your fish
No, you can only sell them, give them away, or put them in tanks in your house.
In my opinion for the fishes feel more in their real habitat and look good in a aquarium!
No, any additional animal put into a confined volume of water will increase ammonia levels and will therefore not keep water 'fresh'.