Yes, you can sponsor your stepson by filing a separate petition. I suggest you work with an immigration attorney

You can processing times here: https://egov.uscis.gov/processing-times/

Put the class of admission in your most recent I-94 (eg. H-1B)

You can check processing times here: https://egov.uscis.gov/processing-times/

After getting married, file I-130, I-485, I-765, I-131, and I-508. An affidavit of support is also needed. It is highly advisable to work with an...

You can apply for premium processing and it will take 15 days

A fiance should marry within 90 days from arrival in the US

H-4 dependent spouses may qualify for an EAD if the H-1B nonimmigrant is the principal beneficiary of an approved Form I-140 or has been granted...

It has to be a government issued ID like a driver's license

The priority date from a previous EB3 I-140 can be retained