How many times can someone co-sponsor?

an individual can sponsor as long as they can support the individuals they are sponsoring and their current household as well. You will need to...

Is there any option for a DACA recipient to legalize the status?

You can adjust status based on an I-130 Petition for Alien relative, however to do so, you must have had original entry as legal or have a waiver.

Do any of the documents for green card application through marriage need to be notarized?

They do not need to be notarized. However all all birth certificates must be certified translations and all foreign documents must be translated

You Will get your EAD in 3 to 4 months, no interview necessary. However you will be asked for biometrics before the EAD ( usually 2 to 3 weeks...

OPt and H1

It depends on whether your H-1B Cap petition was filed as a Change of Status or Consular Notification