As for your first question, there are some TE's who do think that there may have been a literal garden and a literal Adam, and I believe Herev considers this a strong possibility. So, I will let him elucidate if he is about.
As for the flood, you are starting with the premise that a God telling a non-historical story is somehow lying. This simply is not the case. At the time these passages were first inspired, and then first written down (assuming they were inspired earlier than they were written, and told orally for a while first, but this is not positive), people did not draw strict distinctions between literal historical events and semi-historical stories or even legendary stories with only very limited historical foundation. They would not consider it lying at all to pass down important truths in this way. Today, we have a different mindset since the Enlightenment and our more scientific approach to the past. For us, it is either historically accurate or it is "false". This is not how people viewed such things for thousands of years.
So, if the intent of a story is not to provide strict historicity, then it can not be a falsehood when it is not historically accurate.
So, the Biblical flood could have been a local flood in which the events happened very much as described, but from a local perspective. The language would just have been expanded in the telling to make the flood more widespread. Since the purpose of the Scripture is to convey a theological truth, not provide a historical record, there is no "lying" about it. The truths come down to us loud and clear, regardless of whether every detail happened in literal history or not.
Or, alternatively, it could just be God taking a story in circulation at the time (ie, the Sumerian version, which would have been known by Abraham and could have been passed down through his family), and altered it to present the truths HE wanted conveyed. This still would not be a falsehood.