Can I use text content from my old canceled website? Do you think that the new website with this transferred content will be not penalized? Do you think that I have to wait at least half year so the google bots find out that there is no duplicated content on the internet? I assume that rewriting those texts would be safest option.
I personally think there is nothing to worry about.
As an example, I create sites for a certain industry and am in charge of the SEO. The owners are involved in a national organization and for the most part know each other well.
With that, I have created a plugin that generates pages based on specific geo-locations and other than the city names itself, the text content, in most part, is identical.
There are overlapping areas in which 3 businesses show up on the first page organically. I authored the content, and used it as the other businesses content. In areas that overlapped, I would ask, if the first clients are ok with me working on a site with the new inquiring client.
Long story short, if it's not legally infringing on others work, has/had good SEO ranking, there is nothing to worry about. Even if the site doesn't carry the rank over, well written content with proven good SEO practices will always rank or rerank fairly quickly.
One thing I feel a lot of developers do is start worrying too much and contemplate their work.
If you know you aren't phishing or duplicating others work, then there is no scam and search bots will know.. Think about it, Google I believe has over 10,000 math phd's just working on their algorithms to decipher content.
In my opinion, there's not anything to really worry about. Just remember to submit the sitemap.