Can it be trimmed to keep it under 8 ft?

Yes you can, here is some information on how to properly prune it:

https://plantaddicts.com/pruning- arborvitae/#:~:text=To%20prune%20your%20arborvitae%2C%20cut,back%20beyond%20the%20green%20needles

yes you can keep it trimmed to whatever height you want

Yes it can. here is how to trim and care.

https://www.finegardening.com/project-guides/pruning/how-to-prune-arborvitae

here is info on this plant but it is considered a tree not a shrub

https://plantaddicts.com/arborvitae-care/

Yes, but it's best to trim regularly so as not to remove more than 1/3 of shrub at any one time.

Late spring after flowering - After the arborvitae has flowered and before mid summer is the best time to prune back a tall hedge row. The plant can maintain itself after flowering and maintain the height you are looking for. If you are making drastic changes to its height, it is best to cut back a foot or so a year until you have the size you want. This helps keep your cuts in the green wood, which will allow the top of the arborvitae to fill in.

Late Winter - You should cut an arborvitae in the late winter if you are planning a major reduction in its height. The plant stores most of its nutrients in the roots over winter. You want to cut before the nutrients start to move upward to the leaves and branches, but after most of the hard winter has passed. Taking the top off an arborvitae is rare. They don’t grow new leaders, so the top becomes squarish and many find them unsightly. Make sure this is exactly what you want before you take the top off. If you wait until spring, you may be too late, as this can put added stress on your plant.

I haven't seen anything about this plant having flowers.

Louise, I think I should have shortened that link, try this one

https://plantaddicts.com/pruning-arborvitae/

Plants will do whatever they are genetically programmed to do. Trying to maintain a smaller size by regular pruning can be an exercise in frustration. Hedges could be an exception to this, but it can be a pain to trim something so tall. Be sure you will still be up for this in a few years.

You can cut the top off, but expect to have it widen out. It should be gradually cut back to avoid too much shock to the system of the tree and cause it to become misshapen. You would want to trim it back when it is close to or in dormancy-late fall or winter.

You could trim any bush down . every year you trim it down we’re you want it to be after the summer.it will stay the size you want .The trick is to cut new growth off after it gets the size you want .

Yes, you can prune it to the size and shape you want.

Yes, you can but it needs to be gentle pruning. Never remove more than 1/3 of the live foliage area in a season. Trim in the late spring just before new growth.

Yes you can do that!

Yes you can do that!

i would only trim top