Meiji shrine was much nicer, it felt more expansive and historical. Walking through the forested paths and seeing the hi no maru really makes you feel like in you're in the centre of Japan. Sensouji is so crowded and stuffy. While it may be visually more impressive it feels too curated and small.
There is no admission fee to enter Ueno Park, but the various facilities have modest admissions fees (many are around 600 yen). Most museums and other facilities open at 9:00 or 9:30 and close between 16:00 and 17:30, and most are closed completely on Mondays. The hours of the park itself are 5:00 to 23:00.
Sensoji (???) is one of the most significant Buddhist temples in Tokyo. The Kaminari-mon (lightning gate), long promenade (Nakamise Dori) and the temple itself are some of the biggest tourist attractions in the city. There is no admission fee, but you can make a donation if you wish at the temple.
This Shinto ritual of clapping twice is the proper way to purify oneself of impurities, but there are some shrines with a long tradition of three or four claps rather than two.