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Although much depends on the variety of plant you have, in general, it takes 2 years for avocados to develop from blossom to harvest. You may like this article for general information:

http://www.californiaavocadogrowers.com/cultural-management-library/meeting-needs-avocado-trees-during-spring-flowering

Is it possible that your not giving it enough time to finish ripening? And how does it taste, even though it's not as soft as you'd like? Perhaps this is the natural condition of this variety of avocado. Do you know what variety it is? Or is it perhaps grown from seed, in which case it's simply not a really good eating plant. Avocados are usually grafted, in order to have the attributes people are looking for, and plants grown from seed don't grow true to the parent plant, and often aren't very good to eat. Another possibility is that the tree is missing something in its nutrition, so here's an article you can use to check that aspect: https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-tree-growing.htm

Yellowing of leaves is called chlorosis, and it is usually caused by a deficiency of nitrogen and/or some other nutrient(s). Often, the fix is not simply adding more fertilizer, because if the pH is wrong, the plant can't absorb the minerals even if they're present in the soil. Avocados need a pH of 6 - 6.5, but anywhere between 5 and 7 should work. First thing then is to do a simple pH test (an inexpensive home test should work) then adjust pH if needed, then add a bunch of compost and some fertilizer, and make sure your plant has plenty of water. Here are a couple of articles with more information: https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-tree-growing.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm

Generally, these trees do not need much pruning, except when height is an issue. I would not take more than a third of its growth off at any one given time. Prune your avocado tree in late winter or early spring. This article will help you: https://www.gardeningknowhow.com/edible/fruits/avocado/pruning-avocado-trees.htm

It's fine to bring it indoors over winter. As for the roots coming out, this is an indication that the plant is becoming rootbound, and is in need of repotting. That being said, I would recommend waiting until spring to do this - moving up one pot size. Also, you might want to trim the roots when you repot. Here is more information: https://www.gardeningknowhow.com/houseplants/hpgen/learn-more-about-repotting-houseplants.htm

https://www.gardeningknowhow.com/houseplants/hpgen/repotting-stress-treatment.htm

https://www.gardeningknowhow.com/houseplants/hpgen/prune-roots.htm

As long as the tree was a grafted one purchased at a nursery or garden center, then you should be able to get fruit from it.

Unless you live in a somewhat warm region and due to their sensitivity to cold weather, I would have to say no on planting it outdoors, though in a container the tree could possibly spend summers outdoors. These articles should
https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-tree-growing.htm

https://www.gardeningknowhow.com/edible/fruits/avocado/indoor-avocado-plant-care.htm