Answer: If your plants are still in containers--they haven't been planted in the garden yet--then I would remove those first flower clusters. Flowering and fruiting takes up lots of a plant's energy, and you want that energy directed toward root development when you transplant them to your garden. It will delay your harvest a little, but you should end up with much more vigorous and productive plants in the long run.
Peppers like warm temperatures. The plant can become stressed if nightime temperatures drop below 60F--meaning that pepper blossoms may drop.
Generally, it's a good idea to begin feeding indoor-grown seedlings when they get their first "true" leaves. I like to use a dilute liquid fertilizer, mixed at half the recommended strength, about once a week. Fish emulsion is fine; I like to use a product consisting of fish emulsion and kelp for a wider range of nutrients. If you have not fertilized your seedlings at all up until now, that, plus the stresses of hardening off, could account for the yellowing leaves. I would begin a fertilizer program now (using the fish emulsion or a balanced, low-nitrogen ferilizer like 5-10-10), remove those flowers, and get the plants strengthened for the season ahead.
A little boost of fertilizer when flowers first form will help productivity. Just don't over-fertilize (follow label directions carefully) and don't use a high nitrogen fertilizer, or you may end up with all leaves and no fruit. Good luck!
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