Pay stub is not essential; its optional; if you want to further solidify your employment evidence then support your employment letter with the paystubs; But most importantly, its the experience letter that counts
Not required. Just having 2 paystubs preferably towards the end of your employment or one from the beginning and one from the end would be enough.
An entire year's paystubs are an overkill, increasing the case officer's workload to go through them.
Attach other documents that strengthen your employment records such as joining letters , promotions / hike letters , tax returns [ from last year of employment] and of course the reference letter which has the job duties.
Attach a one page LOE at the beginning of each employment record listing the documents that the case officer will find in this section.