Growth speed varies greatly and depends on too many factors but you could see 1'-2'. Or less. Some hydrangeas take 3 years before they grow quickly and reach for the stars. Others must have an already adequate root system and grow quickly on year one.

You do not say where you are located but in the northers states, you could see it 6' or more. Down here in the South where the growing season is much longer, it could get even bigger. Little QF is a more compact version of regular QF. You could use annuals to fill up the bed or other perennials (but transplant them elsewhere if QF gets bigger than you want).

If you are in the northern half of the country, you can grow it in full sun but down here, the leaves can get scorched during the middle of the summer so afternoon shade is a must for me.

I have a QF that is in full sun (in June & July it's more than 12 hours) in a bed that only gets water if we go for more than 3 or 4 weeks without rain. It never looks unhappy and has a long bloom season, so with water in zone 6 I can't imagine you'll have issues.

As far as growth rate, when I planted mine in the fall of 2009, it was perhaps a foot tall. By fall of 2012, it was 5'-6' tall.

I have a Quickfire in full sun and it was the fastest growing plant I have ever seen. It went from just over twelve inches to nearly eight feet in less than four years and I am a very enthusiastic pruner.

Here it is in 2008 at planting, the flowering one in the center-

Obviously I had to remove those plants nearby, as here it is in 2012- the fence is six feet tall-

WOW cearbhaill, what a happy, gorgeous shrub!