mixing light spectrums

You can mix all you want... there is a ceiling to the number of photon/s a plant can handle over 12 or 18 hours of operation. If you notice them drooping for multiple hours and generally slowing growth, it's probably too much light. You can raise the height or knock a couple hours off to combat this, if you think it is "close". If photoperiod, just stay 15hours or more per day and you should avod causing bloom to start. As long as the plant reaches max dli relative to environmental factors, it doesn't matter if it occured over 12 hours or 18.... the plant will shut down as far as receiving light.. it'll droop and wilt. you may even see spots form at top at some point. it's all proportional.. if oyu take 2 hours off from 18, that's 11.1% less photons/s received. Spec sheets are more often erroneous when listing umol/s (intensity) or umol/J (efficacy). if they are a cool white, i'd definitely put the blurple in the middle. The extra Red could easily be a benefit. (again, is heat an issue? is it causing plants to look unhealthy due to "too much light?") watts are a bad measurement to use.. because they vary in meaning relative to umol/s output of photons -- which is what directly causes photosynthesis to occur, not watts/s. The efficacy of your unit wil be an important factor if trying to use watts. cheap stuff you probably want 45-50watts per sq foot. Expensive stuff you can get away with 30-ish watts per sq foot. Over 18 hors i only need 25watts per sq foot due to the efficacy of my lights... if i give more i stunt them and burn them. Other lights may need 40-45 watts/sq ft to be equivalent as far as how many photon/s provided.

You're probably good. A good spectrum mix can always be a good thing, there's one way to find out.

It is common to mix lights especially in flowering when more intense light is needed. In vegging you would not need the extra light.

It wont hurt and if they are proper growing COBs, they will certainly help your plants to flourish.

Are the COBs actual grow lights or some globes you found at the shops cheap? if they are grow lights they yeah chuck em on in and they will def help. But if they are just some cool white or warm white globes you found- nah-they will just cause stretch due to being wrong light color temp. Full spectrum LED COBs are pretty cheap these days so if they are what you have they are fine, if not then no dont use em.