interesting background, is it painted on the tank or is it a printed image? either way I haven't seen in before looks pretty good.
The java fern and anubias you want to plant elsewhere will be fine just floating around in the tank till you get what you want to attach it to.
To tie to rocks and small wood I use the thinnest fishing line I could find at walmart. For attaching to larger pieces of wood or wood already in a tank that I dont want to move, I have used thumb tacs to hold them in place till they took hold then remove the tacs.
I have heard of people using glue, zip ties, rubber bands, etc. Someone else will have to tell you what kind of glue though.