Sometimes hydrangeas will begin to grow like gangbusters. Other times they will grow more slowly. My Glowing Embers has been slow but others have not. It does not mean all Glowing Embers do that, of course. Only that growing slow happens. Since you are new to gardening, get a large shrub instead. The plant label or the website for the nusery will indicate the size at maturity. This is a commercial term that means the expected size at 10 years. They expect a 10 year old specimen to be 4-5' high and 4' wide. Of course, many plants will continue to grow after 10 years so use it to determine if the planting site will look crowded in 10 years and separate them more now instead of later.

If it looks crowded at 15 years then you may have to prune the shrubs now and then. But at least you did not have to do that for the first 14 years!

I have three incrediball planted last spring. I purchased quart pot through online order. They were very small when I got them(Only about 1 feet high max). And there are no bloom from those last year (as expected).
Now they are 3 - 3.5 feet tall, 3 feet wide and with lots of buds all around the plant.
I am pretty happy with them so far since my other hydrangeas have never given me this many blooms.
The place I planted them is a full sun spot, and there is a row of aborvitea trees behind them so they do need to handle root competition with the shallow and dense root of Arborvitae.
The way I take care of them is to give them plenty of water the first year and I fertilize them once in the spring.
Hope this helps!

Let me add photos to illustrate:
2nd year Incrediball hydrangea looks like the following link shows. Note that the new stems grow much thicker and taller than the first year's.

Here is a link that might be useful:

THank you all! Just received 3 2-gallon size from Plant Palette and am about to order 4 more in the quart size based on your thoughts... Really appreciate your help!