Since it's still OK to theorize...

Science can only show what IS, it can not tell us what MIGHT BE, imagination and theorizing are the methods that give us the ability to see what MIGHT BE, it is up to ‘science’ to prove if it IS or IS NOT.

I read that it was Theorized that pre BB there was a whole lot of antimatter.

Personally I think that before the BB there was the BC (big crunch). The ‘constituent’ (fundamental mass) for the newly ‘created’ matter came from the previously existing matter that was fused together in the big crunch.
What is your definition of “antimatter”? Do you consider antimatter as consisting of the same ‘fundamental mass’ as that of ‘normal’ matter but having opposite ‘charge’ to its components, or do you consider antimatter as something totally different from matter?

It brought two interesting concepts to my mind.
Is this antimatter out there expanding into unknown space all around the Universe and is the cosmic background radiation the result of that antimatter reating with the sparse atomic particles it comes into contact with?

That is a good question. My guess is that your speculation may be correct, but I would let ‘science’ come up with definitive proof one way or another.

Can antimatter travel faster than light?

My guess is that antimatter could travel at speeds equal to that of ordinary matter, unless it is composed of something other than fundamental mass with an opposite charge.

I think that the meaning of the words used in scientific explanations should be clearly defined. For instance what is meant by the word “energy”, especially in context of Einstein’s theory of relativity. Also the ‘speed’ of light should be investigated further. Why does a photon travel at a constant speed in a vacuum of space? Does a photon accelerate from its point of origin to the final speed? Why do photons not go faster than the measured speed? What keeps photons going at the measured speed? What is a photon? Why does a photon have a frequency? What is the difference between photons and electrons? Why do electrons have a charge? What is a charge? Why does a charged particle affect another charged particle? Etc.

I have ‘theorized’ solutions to all these questions and many more. If theorizing and imagination was not allowed in investigation of natural laws then how could these and other similar question be answered