Dave, don't fret about asking questions.* That's what these forums are for.* :)*
It's a shrub, but will grow up to 10 feet aka 3.04 meters.
Do I treat this Pieris as a shrub or tree?
When you say "tree shape", I'm thinking you mean that it won't have any leaves on the lower trunks and look more 'tree-like'.* Alot of that depends on the growth pattern of the particular plant.* Pieris does grow tree-like.* You can rejuvenate and get new growth that will be fuller and more shrub-like if you prune the stems close to the ground.* New stems will emerge from the ground.* It's best to do this over a period of 3 to 5 years depending on how large your shrub is.* Pieris blooms on old wood so it's best to prune right after the finsih of bloom as it will set buds for next year shortly after the finish of bloom.* If you prune after that you risk cutting off the following years flowers.* Generally it's best to pinch off the spent flowers.* This site has great pruning info.* Scroll down to 'Tree Like'.* Pieris is also listed under 'Helpful Hints' in Tree-Likes (Thin-out, many small cuts) and Takes heavy thinning or arborizing:.
Can I expect the base growth to thin out and for it to resemble more of a tree shape?
That is a plant grown for it's aesthetic value and not for food or medicine.
Thanrose mentioned that it might be an 'ornamental'. I'm not sure what that means.
Yup!* If one Pieris is toxic, they all are.* Here's the link.
Finally I noticed that under another posting for 'mountain fire Pieris' that the plant should be treated as highly toxic and danegerous. Can I expect my variety to also be toxic?
Don't hesitate to ask more questions.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.