I’m not an expert but your humidity is probably increasing because your plants are transpiring more. You can add a dehumidifier to the room or increase your exhaust fan speed to get rid of the excess moisture. It won’t be too much of a problem now but once they really start flowering you are going to run into mold problems.
You can still very carefully LST if you are running out of room and want the lower branches to get bulkier. At this point you will have to be careful and might need to massage the stem first before the bend but it isn’t too late.
As for nutes, I wait until the stretch is finished to start flowering nutes