A grouping does look good. I'd plant them into the garden now so the roots can get established. Even the hardiest roses can die the first winter if the roots have not had an opportunity to grow into the surrounding soil.
August is a really hot dry time to transplant a potted rose. Unless you water regularly and deep you could lose them especially if the soil falls from the roots when you transplant.
Nature size and planting distance is determined by your growing zone.
Pruning can be easy. After each flush of bloom, allow the flowers to fade some. Use a pair of hedge clippers and remove the dead blooms along with a inch or so of cane to shape the bush. In a few weeks new buds will form along with new growth. You'll have more flowers within a month.
Yearly pruning should be done in spring. Remove winter killed canes and dieback along with any damaged ones. Cut back as far as you want to shape the bush and keep it in bounds.

As much as many rosarians complain about Knock Out being the only roses available in many garden centers, their ease of growing and hardiness encourages many to grow roses again. The desire to grow roses soon entices them to try other varieties.

Go the the following link to find a NJ rose society near you. Contact information will be listed with each society.
They can give you the best info regarding height and planting distances in your area.

Here is a link that might be useful: NJ rose societies

1. Yes, if you have the space, but...

2. In my part of NJ (eastern Monmouth County), Knock Out get to 5' - 7' tall and 3+' wide. I would plant them 4' on center (4' from the center of one to the center of the next one). It will take 2 - 3 years to reach that height.

3. Yes. You can just go through and clip off the old blooms, that's all of the deadheading/pruning that it needs.

4. In the late winter, when the forsythia (yellow flowered shrub) blooms, then you can cut out any dead canes and shape the plant. The first couple of years there shouldn't be much to do.

Unless you are moving, it should be planted in the ground now. August is kind of late to transplant a rose (and it is hot hot hot).

Start with Knock Out. You can move on to something like Rainbow Sorbet next year.

I am a member of the Jersey Shore Rose Society (Ocean, Monmouth, Middlesex, Somerset counties), and I also have a list of all of the Consulting Rosarians in the state, drop me an e-mail and I will send it along.

They are great roses IMO but it would be a shame and a mistake to plant only KOs. There are so many other healthy reblooming roses that deserve a place in the garden!
In a z6 like yours, I would also use some rugosas, like roseraire de l'hay, scabrosa, frau dagmar haartrup and some of the pavement rugosas. They are too carefree, and many also make hips. In my zone /z8a) they also bloom 2-3 weeks before the KOs :-)

Training wheels, I start everyone off with training wheels (Knock Out, in this case)...

And this year, in my area, the Knock Outs started blooming before the rugosas. I grow Blushing Knock Out, and it will be lovely in a day or so when it will be covered with blooms.

I'd get it in the ground now. If I don't trim mine, they get at least 7' tall. The canes are trunks.

I'd get that rose in the ground and let her get established. I have a pot garden for now till we get to our house. I have knock outs and they don't do well for me in pots even in the summer. I may have lost 2 of the three. I have only one of the three that has any visible green left on the canes. Only my hardiest roses have any leaves because this winter has been long. The knock outs just don't do well in general for me and produce few flowers. Yours should do fine in the ground but give it a chance to get established before winter. Carefree Beauty is one that does really well for me and she's pretty and hardy. You might want to give her a shot too.

Knockouts are a good place to start!

Best of luck with your roses; there are lots of folks on this forum who can help you out with good info.

Congratulations on the first rose--a good choice for your climate!