Yellow leaves black spots -- soil problem?
It is likely a fungal problem.
They can tolerate just about any range of pH, but prefer to be around 6.5 to 7. Dolomitic lime will help keep the pH balanced, but you will need iron sulfate to bring that down just a bit, along with killing the fungus responsible for the issue.
The tree is in a very big pot and its not root bound
This can also happen due to a lack of light. Make sure to give this full sun, or plenty of horticultural lighting if this is indoors.
This article will help you with the care of citrus in container: https://www.gardeningknowhow.com/edible/fruits/lime/potted-lime-trees.htm
It also has scars on the bark where it looks like some animal has chewed on it, The tree looks healthy and strong. I painted the tree with tree paint and that seems to have stopped the abrations'
If these are not fertilized each year with a citrus fertilizer, then this is likely the issue. Here is an article that will help: https://www.gardeningknowhow.com/edible/fruits/citrus/fertilizing-citrus-trees-best-practices-for-citrus-fertilizing.htm
Can I plant my Meyer Lemon Tree in the sandy soil I have in my backyard without having to add something else to it?
They can handle sandy soil, but they will do much better if you amend it with compost, at the very least.
These articles will help you: https://www.gardeningknowhow.com/edible/fruits/lemons/growing-meyer-lemons.htm
https://www.gardeningknowhow.com/edible/fruits/lemons/how-to-grow-a-lemon-tree.htm
and does it like direct sunlight.
I don't find anything that smells like limes other than limes or wild lime. My next thought is you need information on how to get it to fruit:
have never grown or maintained citrus trees before and need to learn.
You can find a wealth of information on this site, at the library, online, books, etc.
Here are some articles that may help:
https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-tree-fruiting.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/tip-on-water-requirements-for-citrus-trees.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-blooming-season.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/different-types-of-citrus-trees.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/tip-on-water-requirements-for-citrus-trees.htm
https://www.gardeningknowhow.com/category/edible/fruits/citrus
My trees are just a year old.
There are many fungal/bacterial infections that cause damage to citrus. The first thing will be to change the care of the tree.
You will need to make the environment more suitable for the tree, and less suitable for the infection, since they prefer quite different environments. This will mean letting the soil dry out, very thoroughly and completely, down to about 3 or 4 inches between watering. It may also mean improving air flow to the area around the tree, while preserving the humidity levels. This can be achieved with a fan and humidifier, to keep the humidity around 40-50 percent.
Next will be a treatment. A fungicide or bactericide may be necessary. These articles will help:
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
https://www.gardeningknowhow.com/garden-how-to/info/applying-bactericide-to-plants.htm
Two things that will mitigate many of these issues, and are good to have around for citrus- DOLOMITIC LIME and IRON SULFATE. Applying once per year, according to packaging instructions, and whenever there is an infection will help to resolve the issue.
Here is a collection of articles that will help you to care for citrus: https://www.gardeningknowhow.com/category/edible/fruits/citrus