1. obviously one can both work and study at the same time. Overlap is totally fine. Only gaps are a problem. In other words: You can have a month in which you did 10 things at the same time, just make sure that you have no month where you didn't do anything.
2. You are not giving enough details to answer this. When did you become PR and so on. I am copy pasting the text from the official guide below. Make sure you read it in full. If
after reading it in full you still have a question, explain which part is unclear.
3. Again you are not providing essential details. Was the degree in your home country in English? Note: The whole program must have been conducted in English and you need proof that it was. If you say "I studied English 11 and 12 here", do you mean that you took a single course in English? Only if you attended a fully English secondary school or college program in Canada does it count. To clarify: you must have taken more than just English lessons. You must have taken ALL your courses (Bio, History, Music, whatever you studied) in English.
4. The eligibility period is the past five years. the date you arrived is irrelevant.
Before filling out and submitting your application, make sure that you read
the entirety of the application guide
https://www.canada.ca/en/immigration-refugees-citizenship/services/application/application-forms-guides/guide-0002-application-canadian-citizenship-under-subsection-5-1-adults-18-years-older.html
Yes it is long, but it seems you haven't done so so far, so make sure you check every detail.
===
Text regarding police certificates:
- In the past four (4) years, if you spent 183 days or more in a row (since the age of 18) in a country (other than Canada), you must provide a police certificate from each country. Indicate in the chart the name of each country and provide a police certificate. If you can’t get a police certificate, tell us why. The following examples may help you answer this question.
Example 1
You lived in France for one year (365 days) before you became a permanent resident 3 years ago. You did not travel to France after you became a permanent resident. You would answer “Yes” to the question and you would need to provide a police certificate from France if you did not provide one with your immigration application. If you provided a police certificate from France with your immigration application, tell us this in the box provided at Question 10b.
Example 2
You became a permanent resident three years and nine months ago. In the past 4 years, you lived in Brazil for 3 months (90 days) before you became a permanent resident and you returned to Brazil to visit family for 4 months (120 days) after you became a permanent resident. You would answer “No” to the question and you would not need to provide a police certificate from Brazil because you did not spend 183 days or more in a row in Brazil.
Example 3
In the past 4 years, you took 10 trips to the United States of America (USA). Each trip lasted 3 weeks, for a total of 210 days. You would answer “No” to the question and you would not need to provide a police certificate from the USA because you did not spend 183 days or more in a row in the USA.
Example 4
In the past 4 years, you travelled to Singapore four times for work. The first trip was for 30 days; the second trip was for 200 days; the third trip was for 60 days; and the fourth trip was for 120 days. While in Singapore, you took a trip to Malaysia (10 days) and Thailand (10 days). You would answer “Yes” to the question and you would need to provide a police certificate from Singapore because your second trip was more than 183 days in a row. You would not need to provide police certificates from Malaysia or Thailand.
Example 5
In the past 4 years, you took one (1) trip to Europe where you visited Portugal (5 days), Spain (7 days), France (10 days), Belgium (3 days), Netherlands (3 days), Germany (21 days), Switzerland (7 days) and Italy (21 days). You took a second trip to Europe where you visited Ireland (14 days), Scotland (14 days) and England (21 days). You went to Germany for a business trip that lasted 60 days. The total time you were outside of Canada was 186 days but you were not in a single country for 183 days or more in a row. You would answer “No” to the question and you would not need to provide police certificates from any of the countries.
Note: If you were in your country of origin immediately prior to becoming a permanent resident and landing in Canada and this time falls within this four year period, you are not required to provide a police certificate. Please indicate this in the explanation box.
The police certificate must either have been issued:
- after the last time you were in that country; or
- no more than 6 months before the date you sign your citizenship application
Visit, How to get a police certificate for specific and up-to-date information on how to obtain police certificates from any country.