when those leaves on the bottom die, the plant is usually telling you , it's out of Nitrogen in the soil
a lot of new growers make the mistake of giving the plant bloom boosters, which are worthless without a N source.
Less is more with bloomboosters
know that the soil has around 1 month of nutes in it after transplant (more if it's really big)
so if you transplant, then flower, 1 month or so you need to supplement nitrogen or you'll see the bottom leafs fade
best ways to combat this are either top dressing the soil every 2-3 weeks, if you dont have a liquid fertilizer, or adding liquid ferts that include enough N for the plant ( i like npk around 3-1-2 , 6-2-4, ect...)
also if you think the bottom is light deprived, throw a CFL bulb in there. You can use a bed lamp or something without a shade just till it's done.
always try to avoid chopping things off, yes the plant can handle it but I believe its counter productive and unnecessary; you aren't "boosting" yield doing that unless you have an overabundance of foliage that wouldn't have gotten adequate light unless you cut it
Don't worry about flushing, worry about over ferting
IMO , defoliation doesn't have a place. Some people say they do it, but I always think there's a way around it. They say to each his own