If your enclosure has only been set up for 2 weeks, it may be that the one plant that doesn't seem to be doing well is still acclimating. Some plants, especially ferns, will have some die off during the first few weeks. Most are going from rather low relative humidity to a much higher humidity in the enclosure and they need to adjust. It is highly doubtful they it is from lack of nutrients. Symptoms of nutrient deficiency normally take longer than 2 weeks to show.
Your plan for revamping the enclosure seems sound and should provide a happy home for your inverts.
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