The institutions of the Qing were inherited from the Ming and the Qing kept much of the Ming structure intact. Traditionally, rank one positions were mostly honorary and prestige positions that carried very little power, but people who held these positions often concurrently held other positions of power.

According to 艾永明 清朝文官制度 (Institutions of Qing Civil Officials) and Charles Hucker's A Dictionary of Official Titles in Imperial China:

Rank 1a:

• 太師 Grand Preceptor
• 太傅 Grand Tutor
• 太保 Grand Protector
• 殿閣大學士 Great Scholar of the Palace/Grand Secretaries

Rank 1b:

• 少師 Junior Preceptor
• 少傅 Junior Mentor
• 少保 Junior Protector
• 太子太師 Grand Preceptor of the Crown Prince
• 太子太傅 Grand Tutor of the Crown Prince
• 太子太保 Grand Protector of the Crown Prince
• 協辦大學士 Assisting Grand Secretaries
• 各部院尚書 Head Ministers of the Six Ministries
• 督察院左右都御史 Left and Right Chief Censors of the Imperial Censorate

From the Qing Shi Gao, Vol 114:

內閣 大學士，滿、漢各二人。初制，滿員一品，漢員二品。順治十五年，改與漢同。雍正八年，並定正一品。協辦大學士，滿、漢各一人。

Translation: Grand Secretaries of the Grand Secretariat, two Manchus and two Han. In the beginning, the Manchus were rank 1a and Han were rank 2. In the fifteenth year of Shunzhi, [the Manchu] were changed to be the same as Han. In the eight year of Yongzheng, both were set at rank 1a. Assisting Grand Secretaries, one Manchu and one Han.

吏部 尚書，初制，滿洲一品，漢人二品。順治十六年改滿尚書二品。康熙六年復故，九年仍改正二品。雍正八年俱定從一品。各部同

Translation: Ministry of Personnel, Head Ministers, in the beginning the Manchu were rank 1 and Han rank 2. In the fifteenth year of Shunzhi, the Manchu were also changed to rank 2. In the sixth year of Kangxi, the early custom was restored, but in the ninth year, it was changed back to rank 2. In the eight year of Yongzheng, they were changed to rank 1b. This applied to all the six ministries.

In the Qing, important government posts was overseen by both a Manchu and a Han. So for each of the Six Ministries, there were two Head Ministers, or twelve total for all six. There were six Grand Secretary positions, each occupied by four Grand Secretaries with two Assistant Secretaries. So assuming, all the positions were filled, the Qing would have fifty-nine rank 1 officials in Beijing.

In addition, we also have Viceroys for the various provinces with ranks of 1b. According to the Qing Shi Gao, the Qing had eleven Viceroys:

• Viceroy of the Northeast Three Provinces
• Viceroy of Zhili
• Viceroy of Liangjiang
• Viceroy of Shaan-Gan
• Viceroy of Minzhe
• Viceroy of Huguang
• Vicery of Sichuan
• Viceroy of Liangguang
• Viceroy of Yungui
• Viceroy of Water Transportation
• Viceroy of Rivers and Canals

So, another eleven provincial adding onto the fifty-nine Beijing officials would give us a total of seventy rank 1a and 1b officials. However, it's important to keep in mind that these posts were not all filled up at one time. I can't give you the exact number since I don't have access to that kind of data.

As for the perks, they had a lot of prestige and power, and also were paid the highest salaries.

Can I ask for clarification?

Do you mean in total ever during the times you gave (e.g. how many served under Kangxi throughout his reign), or do you mean, at any given time, how many were currently standing (i.e. what's the usual number of officials)?

Also, though much less importantly, do you mean primary first-rank officials or both primary and secondary first-rank as well?

You don't need to reply to this if you see it. If you could just edit it into your original description that'd be better because then I can delete this comment.