Answer: I'm glad your tree is beginning to show some signs of life! Like most houseplants, citrus thrive in a normal household temperature range of 70 degrees during day, to 55 to 55 degrees at night. Citrus trees prefer full sun from a southern exposure. If that's not possible, you can supplement the light by installing 40-watt fluorescent shop lights above the plant, keeping it on 14-16 hours a day. As for moisture, you'll need to keep the soil evenly moist and since most interiors are quite dry during the winter months, mist your plant often -- daily if you can. Give your lemon tree a shower occasionally to remove dust from the leaves.
Since your tree is in a container, and it's easy to overdo feeding with the roots restricted in a container, I recommend using a half-strength dilution of liquid fertilizer and applying every 2-3 weeks year around. This method will provide a constant source of nutrients without the concern of over-fertilization.
Yes, the number of leaves on the tree is important to supporting fruit, but it's likely your tree will drop some of the blossoms on its own before they set fruit. I'd allow it to determine whether or not its capable of supporting the fruit that develops. You can help transfer pollen by visiting each opened flower with a small artist's paintbrush. Simply move the brush around inside each flower, going from one to another. That should move the pollen onto the right places and start the production of fruit.
Best wishes with your tree - hope you get some fruit!
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