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Unfortunately, your photo did not come through. I am unable to assess the damage.

It sounds like the sudden change in light has shocked the tree. Hardening off will be required to prevent environmental shock in the future. This just means that the tree will need to adjust to outdoor life, slowly.

Usually, they will recover with proper watering. Just make sure to let the soil dry out down to about 2 or 3 inches, thoroughly, between watering. This will prevent rotting issues that will, ultimately, kill the tree.

Prune any dried growth, and leave the stem to grow upwards. You would not want it branching that low to the ground. It would be a hassle when it gets mature.

Here are some articles that will help:

https://www.gardeningknowhow.com/houseplants/hpgen/move-houseplant-outside.htm

https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-tree-growing.htm

I see your problem. It looks as though the tree may need some thinning. Here is more on pruning:

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=12051

It also may be getting too much nitrogen, which would explain the heavy green growth and minimal fruit.

https://www.gardeningknowhow.com/edible/fruits/avocado/how-to-fertilize-avocados.htm

Here's an article that may help. https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-tree-with-no-fruit.htm

Here is a link to an article with information about grafting avocados: https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-tree-grafting.htm

For local information you may want to contact an agricultural program connected with a university in your area.

If the veins in the yellowing leaves are green, you may need to feed the tree with an iron-rich fertilizer. If the leaves are turning completely yellow, the tree may be lacking nitrogen. You may want to test your soil and see if its lacking in either of these elements. Make sure you remove any dead leaves, stems and debris around the plant. You will also want to examine the leaves and stems closely for insects and other possible problems, which are described in this article.
https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-pests-and-diseases.htm

It has grown leggy probably because it needs a brighter window or some light from a flourescent lamp. No reason it can't go in a pot. I like this article because it gives some details about how to grow the plant in a pot: https://www.gardeningknowhow.com/edible/fruits/avocado/indoor-avocado-plant-care.htm

Be sure to pay attention to the pot size recommendations. Too large and it can cause your plant to be overwatered.