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It could be rust mite damage or citrus melanose. Here is more:

https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-mite-problems.htm

https://www.gardeningknowhow.com/edible/fruits/lemons/pests-of-lemon-trees.htm

https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-melanose-fungus.htm

This sounds like the added nitrogen is too much. It can be slightly difficult to remove this excess nitrogen, but the easiest way is with nitrogen consuming plants.

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/too-much-nitrogen-soil.htm

I'm not seeing any signs of infestation. It doesn't seem like a nutritional deficiency, since you have it in specific soil.

You could check pH, but your area should be experiencing some seasonal changes at this time. This would explain yellow foliage. Leaves can fall off with a more drastic change, but it won't harm anything. It'll regrow leaves.

They are likely not hardy in your area, unless you purchased one for your area, specifically.

Here are some articles that will help:

https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-leaves-turn-yellow.htm

https://www.gardeningknowhow.com/edible/fruits/lemons

Yes, that is the chrysalis of the beautiful Giant Swallowtail butterfly, the largest butterfly in the U.S. Its caterpillar eats the leaves of its host plant, citrus. Its feeding won't kill your lemon tree and the leaves should grow back. You may want to get some other host plants in the citrus family to divert them from your lemon tree.

Here are some other host plants:
herb rue - Ruta graveolens
Prickly ash – Zanthoxylum americanum
Hop tree – Ptelea trifoliata

Here is info and a photo of the Giant Swallowtail and its caterpillar.

https://entnemdept.ufl.edu/creatures/citrus/giantswallowtail.htm

I see the typical signs of Phyllocnistis citrella. Those winding trails point towards an infestation. This will be best controlled with beneficial predators like the parasitic wasp.

https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-leaf-miner-damage.htm

Unfortunately, your photos did not come through. I cannot see the issue in question and I'm not sure what is meant by "shinny". However, I will assume that you are referring to a shoot coming from the base of the tree. This will indicate that the grafted rootball specimen is "waking up". It can be a sign of stress that your tree is experiencing, but it can just be a sign of a vigorous root ball, as well. This really depends on the health of the rest of the tree.

Since the tree is producing fruit, I will assume that these "suckers" are a normal part of your rootball. They will stop as the tree ages. Just continue to remove them as you see them.

https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-sucker-removal-and-tree-sucker-control.htm

These articles will help you with citrus care:

https://www.gardeningknowhow.com/edible/fruits/citrus