Wow I wish mine was doing as well -- all those new flower buds will open soon and if there is sufficient pollinator activity (bees, etc) you should see more baby lemons. If you don't see insects working the flowers, you may need to assist with cotton swab or soft watercolor or makeup brush.
The lichen in itself I don't think is a big problem, but it IS growing where there is a broken branch tip. It's never a good idea to leave them like that. You should cut those jagged dead stubs off with sharp pruners or a knife for a clean cut just above where the branch divides.
I'm thinking I see signs of mites too, but I'm not sure. Maybe someone else can make positive ID.
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