221G, white slip and returned passport for H4 stamping

[GSRVisa]

Im on F1 visa and it will expire in March 2019, I did multiple masters in USA and planned to convert from F1 to H4. Documents asked was all transcripts and job responsibilities on OPT and CPT, hours worked per work and employer letter and client location and marriage certificate, photos, description and timeline of courtship and marriage. Interviewer asked me send an email with those scanned copies.
How long does it takes to process H4 and can i apply another H4 visa while 221 g under process ?