Shrinkage and advice please

Hi Everyone. I have just joined the forum and so glad I found it. I am just getting started. I have ordered all the things I feel I need to make a start and just waiting for everything to turn up. Having watched many videos on you tube and been in touch with a few people I am more confused than ever. First I will explain what I do and then what I want to achieve. I make many different things in hardwoods that I sell at craft fairs and these things include name signs, house signs, various plaques, candle holders and many other things.

With the polymer clay I want to start off in two ways. Firstly I want to fill the letters I cut out from inside the wood. I cut the letters using a scroll saw, which means that each letter goes all the way through the wood, if you hold it up to the light you will see daylight through the letters. Ideally I would like to use a clay that does not need to be baked in the oven but I have been told that all air dried clay shrinks and if this is the case the clay in the letters would just fall out, defeating the object of the exercise. If I use oven bake clay I am concerned about burning the wood, although initially I shall experiment using off cuts. I also understand that I will need to make a tent of baking foil over the items I bake. The wood I use is 20mm thick and the average width of the letters is 10mm. When I start I feel it may be best to overfill the letters and then when hardened sand the letters off so they are flush with the wood. One person told me to use Fimo soft and said it does not shrink, would this be the best choice.

The other thing I want to do with the clay is to make some embellishments, such as various flowers and hearts. On some of the name signs I make they are fixed to a base and on the base I would like to fix maybe a couple of roses and maybe a heart in the middle and on the baby boy name signs maybe a teddy bear with a heart. I don't really see any problems with this aspect and it seems to be quite straight forward. I have bought the baking trays and the foil etc. I presume I would use super glue to fix them to the wood. I would also like to glaze the flowers etc so what would be the best one to use. Sorry to pose so many questions but I am a raw beginner. Many thanks in advance.