1. I wouldnt worry about lower leaves yellowing. All die some day.
2. Do you have a fan on them? Couldnt see but the stems look nice n thick.
3. Look healthy enuff, so young I woulnd't fert yet.
4. Plant height doesn't mean a lot for flowering. Look for alternating stem growth.
5. Yep you might want more light for flowering.

If you plan on harvesting Aug 21, better start the 12/12 right now.

That will give you exactly 8 weeks.

Better to have a low yeild quality bud than bigger immature bud that was picked way too early.

Good look.