craftgrrl | How to question- 3D collage in frame using branches and paint

I have a very exciting idea, but I have 2 questions.

Basically, I have some large frames from work that we got rid of when we moved. My plan is to take the photo out, put a new background in, and then take some tree branches, fake flowers, little charms, and make a 3-d collage in the frame behind the glass (it is a very deep frame). If this works out, I have a couple more frames-- I am planning a 'marsh' scene with cat-tails and willow stalks, and a beach scene with sand and things.

Here are my questions-

1) If I take some branches and put them in the frame, do I need to do anything to them first? Should I bake them in the oven to dry them or kill bugs? Do I need to laquer them so they don't fall apart over time? Basically, what do I need to do to make it last and not fall apart over time.

2) This is a do-you-remember thing, but I can't find it... someone had a technique of taking a canvas and painting it, and then somehow soaking tissue paper in paint and glue or something and sticking it to the canvas to make this crinkly texture that was completely amazing. Did anyone save the instructions for that?

I really appreciate any help-- I feel like I have been stuck in a crafting rut for a long time, and suddenly I am so excited I almost took off work to start this. I will post photos when I finish!

Thank you!