Bottom leaves issue

I don't think you need to worry, during flowering the lower leaves start to yellow because they don't receive much light and the plant itself begins to feed on them since they are no longer useful without light. It's common to see the lower leaves yellowing and dying as flowering progresses. The burnt tips on all your leaves are due to a slight nitrogen overfeeding, nothing serious, it's very common for this to happen, it won't affect anything. I see that the lower leaves have some spots in addition to these things I'm mentioning, I think this could be due to two things: 1: when you water with your nutrient solution, some drops splash onto these leaves and cause the burns. 2: slight calcium-magnesium deficiency. I'm more inclined towards number 1, but maybe a more experienced user can tell you this with certainty. Overall, the plant looks good, I wouldn't do anything, I wouldn't remove the affected leaves that you're worried about. I would just keep going as you have been so far.