Setting screws in concrete while it is still soft -how do I use epoxy in this case? Can I ? Should I?
Setting bolts in wet concrete is a standard practice, and using a board to hold them in place is a good idea.

You absolutely do not need any epoxy when setting into wet concrete. I don't know what effect that would have, but its certainly redundant. Epoxy is used when setting anchors into preexisting hard concrete which has been drilled.

Generally you wouldn't use regular hex-head bolts for this, you would use an actual anchor which would look something like this:



The bend prevents both pull-out &amp; rotation once the concrete cures. These come in varying lengths depending on your application (eg 8, 10 inches) - but they are inexpensive so you can just err on the side of "bigger is better" assuming you have enough concrete depth (which in a post should not be a problem).

Where I live I think these are sometimes referred to as "J-bolts".