I only took one asprin, will I get reyes syndrome?

Unlikely. Millions of people take Aspirin every day without getting reyes syndrome. There is a small chance of reyes syndrome developing when Aspirin is taken by a child with certain viruses, which is why Aspirin is rarely recommended for fevers in children any more (except under certain circumstances).
No. Reye syndrome emerged in the 60's and has almost disappeared. When we realized a link between flu/chickenpox & aspirin products, we quit using it is kids. At present it is rarely used in anyone under 16 except for specific conditions.Adults take aspirin all the time with no link to this disorder. Take it if you wish, but there are often more effective alternatives available.
Highly unlikeky. Usually happens in a few children under the age of 12 who have a viral infection and are taking aspirin and not in adults.