Green card holder parents filling for kids

[mrcp2017 4]

I am green card holder and I would like to file for 4 sons living in Pakistan they all are unmarried but above 21 years of age.I have few questions?how long does the whole process takes from filling I-130 upto them receiving visa from US embassy in Islamabad on average?how long does uscis take to process I-130 for kids above 21 years of age?how long does uscis takes to send case to nvc?how long does nvc take to contact us after receiving case from uscis?how long does nvc take to send case to us embassy?how much should I be earning in year to sponsor my 4 kids?is affidavit of support required both for NVC and embassy?do We need to submit affidavit of support both for NVC and embassy separately at their respective stages?other than previous 1 year tax returns and affidavit of support is there any thing I need to submit to meet financial requirements?what is the total cost of whole process?I apologize if someone has answered all these questions earlier but I have great confusion all these steps so I want to mentally prepared for them in advance unfortunately I cannot afford lawyer once again I apologize for any kind of inconvenience 

[HRQX 4,145]

12 minutes ago, mrcp2017 said:

how long does nvc take to contact us after receiving case from uscis?how long does nvc take to send case to us embassy?

F2B category can take about 6 to 8 years. Periodically check the most recently released Visa Bulletin: https://travel.state.gov/content/travel/en/legal/visa-law0/visa-bulletin/2021/visa-bulletin-for-april-2021.html

[Boiler 45,525]

Sponsorship arises when their priority date is current

[HRQX 4,145]

1 hour ago, HRQX said:

Periodically check the most recently released Visa Bulletin:

https://travel.state.gov/content/travel/en/legal/visa-law0/visa-bulletin.html