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Most will reach a mature height of 10-15 feet, so this should be a easy height to accommodate within a large planter. If you feel you need to go larger, it will not hurt to do so.

Here is some links that will help you.

https://extension.unh.edu/resources/files/Resource000594_Rep616.pdf
https://www.gardeningknowhow.com/ornamental/trees/arborvitae/growing-arborvitae-trees.htm

Bt (Bacillus thuringiensis) products sprayed in the spring can be successful in the control of bagworms. In addition, hand pulling or power washing the 'bags' off the plant may be an adequate form of control. Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/plant-problems/pests/treatment-bagworms.htm
https://www.gardeningknowhow.com/plant-problems/pests/using-bacillus-thuringiensis.htm

Daily water during this duration is likely to much for the plants. Regular and deep watering for the first couple of months is important, then you can back off.
Soil should be well draining but have a good loamy soil.
Proper planting depth is important and a wide enough planting hole dug for root growth.
Keep in mind that a new planting may sometimes show stress and have some yellowing of leaves, but if the plants continue to show more yellowing it is likely root rot.
Plants will not survive if the draining or overwatering is not corrected in time.
Also make sure you inspect the plants for insects. Arborvitae can become infested with Aphids and yellowing leaves can be a symptom.

https://www.gardeningknowhow.com/ornamental/trees/arborvitae/growing-arborvitae-trees.htm

The packing material is generally paper that is moistened. Make sure this stays damp, but avoid drenching it.
Use some plastic to wrap the bare-root plants and store in a cool, dark place--basements, garage or sheds.
Keep them in temperatures between 40 and 60 degrees F.
This will keep your plants dormant and you can safely delay planting for about 1 week.

https://www.gardeningknowhow.com/ornamental/trees/arborvitae/growing-arborvitae-trees.htm

I'm concerned you may be overwatering your Arborvitae. If the soil is constantly wet, the roots may become water logged and this will lead to root rot.

Though watering is important in the first few months after planting, you should begin to taper off on the watering schedule.
Also make sure the soil is draining. If you dig down about 8 inches and the soil is wet and soggy, you are likely watering too much.

I would also inspect the plants more closely for signs of pests or disease.
Boring insects can also girdle a tree and disrupt the trees ability to take up water. Look for small holes in the trunk and small piles of sawdust.

Application of spring fertilizers are generally not an issue, as the plants are actively growing.
I don't think the Treetone is part of the issue.
Here are some articles with more information.

https://www.gardeningknowhow.com/ornamental/trees/arborvitae/growing-arborvitae-trees.htm
https://www.gardeningknowhow.com/ornamental/trees/arborvitae/winter-damage-to-arborvitae.htm
https://www.gardeningknowhow.com/ornamental/trees/arborvitae/fertilizing-arborvitae-trees.htm