Should I buy a bus pass?

Only if you are staying near the station and visiting multiple distant sites. Otherwise, IC cards like Suica or Pasmo are much faster and easier to use.

What is the best way to avoid crowds?

Visit 'secondary' temples located slightly further from the main bus stops. Sites like Honen-in or Gio-ji are significantly quieter than Kiyomizu-dera.

Kyoto: How to Plan an Efficient Temple Hopping Route

Group your temple visits by geographic cluster—Arashiyama in the west, Higashiyama in the east, and Northern Kyoto—to avoid spending your entire day on a bus. Dedicate one full day to each cluster to minimize transit time and maximize exploration.

Map your clusters. Divide Kyoto into three distinct zones. Zone 1: Arashiyama (West), Zone 2: Higashiyama/Gion (East), and Zone 3: Northern Kyoto (Kinkaku-ji and surroundings). Never attempt to cross the city from west to east in a single day.
Start at 7:30 AM. Kyoto's popular temples open at 8:00 or 9:00 AM. Arriving 30 minutes before opening allows you to beat the tour buses. Use this time to walk the approaches or quiet gardens.
Use the train, not the bus. Kyoto buses are notoriously crowded and slow during peak season. Use the JR lines, Keihan line, or Hankyu line to get near your cluster, then walk or use a short taxi ride to reach the temple gates.
Limit to three major sites per day. Visiting more than three temples leads to 'temple fatigue.' Aim for two major sites in the morning and one smaller, quieter garden or shrine in the afternoon to pace yourself.

Should I buy a bus pass?: Only if you are staying near the station and visiting multiple distant sites. Otherwise, IC cards like Suica or Pasmo are much faster and easier to use.
What is the best way to avoid crowds?: Visit 'secondary' temples located slightly further from the main bus stops. Sites like Honen-in or Gio-ji are significantly quieter than Kiyomizu-dera.