This article has the answer to many of your questions.
“The new study, however, is the first to directly show that the spike proteins themselves are able to cause harm, and also confirms that COVID-19 is primarily a vascular disease that damages blood vessel walls.”
So this study shows neatly that the spike protein is toxic in the conformation it is made mimicking that found in the virus, but without being able to replicate. It also shows what has been suspected, that Covid-19 is a vascular multisystem disease and not limited to the lungs.
” The Pfizer and Moderna vaccines produce the full-length spike protein. Pfizer studied several formulations initially, but found that the full length protein vaccine had fewer side effects and was better tolerated than other vaccine candidates, so that is the one they went with.”
So that answers your other question about what bit of the spike RNA is used, it is the whole length.
And why therefore is the spike virus protein toxic but not the vaccine generated protein: the answer appears to be that again the conformation of the protein produced by the vaccine is antigenic and and therefore produces antibodies, but is not able to interact with the ACE receptor as that of the virus can and therefore affect the target cells. I also read somewhere else that the amount of free spike protein that is detected in the circulation is tiny and unlikely to cause widespread damage.
“After the Pfizer vaccine full spike proteins are expressed on the vaccinated cells for presentation to the immune system. But the vaccine-induced proteins do not appear to cause any harmful effects. This may be because the vaccine is administered in the muscle, and so muscle cells are the ones taking up the mRNA and making spike proteins. There is a vigorous immune response which neutralizes the spike proteins before they can cause any harm. This is very different from a virus replicating throughout the body.”