NASA’s Transiting Exoplanet Survey Satellite (TESS) mission launched in 2018 and has since observed more than 90% of the sky and discovered more than 6,000 planet candidates of many sizes, temperatures, and orbital periods. Hot Jupiters, in particular, have benefited from TESS since these planets are uniformly distributed throughout the sky and produce large transit signals. Many questions remain about this enigmatic class of large gas giants orbiting extremely close to their host stars regarding their formation and evolution. My dissertation leverages TESS to investigate the potential formation mechanisms of hot Jupiters and applies relevant planet discovery techniques to a collection of planet candidates that would be most amenable, or “best-in-class,” for atmospheric characterization with JWST. First, I performed a uniform search for nearby companion planets to hot Jupiters observed by TESS in its first year of operations. The lack of planets nearby hot Jupiters in their planetary systems has long been thought to be a fingerprint of their dynamically active formation history, although a recent set of discoveries of nearby planets in three hot Jupiter systems has challenged this notion. I developed a custom-built search, vetting, and validation pipeline to detect additional transit signals in TESS light curves of hot Jupiter systems and evaluate the planetary nature of each. This study found a host of new transit-like signals but none were deemed to be caused by planets, reinforcing the idea that companion planets to hot Jupiters are rare. I also estimated the expected rate at which hot Jupiters should have companions and found it to be 7.3+15.2−7.3%. Second, I continued the search for additional planets in hot Jupiter systems as TESS continued to observe the sky and discovered a new signal in the WASP-132 system. I vetted and statistically validated this signal to demonstrate that it is indeed from a new planet, dubbed WASP-132c. This planet orbits interior to the hot Jupiter WASP-132 b and constitutes only the fourth such system discovered at the time. I performed some initial analysis on the limited sample of hot Jupiters with nearby companions and found evidence suggesting that systems with this architecture predominantly have an outer hot Jupiter beyond the ∼3 day orbital period pileup with an inner companion. This may be due to a number of factors, including physical and observational, such as formation mechanism or the bias towards short period planets of transit surveys. Finally, I leveraged the planet discovery, vetting, and validation techniques I had applied to the search for companions to hot Jupiters to perform a large-scale validation of over 100 planet candidates discovered by TESS that were deemed “best-in-class” for atmospheric characterization with JWST. This included the synthesis and ranking of all planets and planet candidates by observability with JWST into a single sample and then performing vetting and validation analyses on those that were candidates. In total, I statistically validated 22 planet candidates and marginally validated a further 35. I present the final best-in-class sample as a community resource for future JWST observations.