Hi Pat,
A few comments regarding your situation.
1. I have had good luck with ‘like adhering to like’, even if they were different brands. For example, I have used one brand’s epoxy on another brand’s epoxy and have not had problems with things adhering. From what I know about polyester and epoxy, I would expect it to work there too, assuming the first layer had completely cured. I haven’t specifically tried this though, so proceed with caution.
2. As for the wood, epoxy would be my choice to use in this project. Polyester resin will shrink too much after curing. It may even shrink so much it doesn’t stick to the wood! Polyurethanes can be used with wood, but your wood will need to be dry and sealed first. Polyurethanes hate moisture.
3. As for ‘seamlessly’, yes, they will attach, but a seam may show depending on how you color it, if you color it, etc. Pouring the next layer while the first layer is curing will minimize the seam.
Good luck!