I have never shot an AR. I am assembling my own, planning on buying a complete upper. I have a lower and lower parts kit. My budget is in the PSA or JoeBob range.
I don't know if what I want is practical in one upper, or even at all.

I want a light rifle for me to shoot with my wife and kids, all who are a lot shorter and weaker than me.

I want to put a scope on it and shoot groundhogs. I have hanging steel plates I can shoot out to 500 yards.

Questions:

Is a cheap 16" barrel significantly less accurate than a cheap 18 or 20 inch barrel?

Is a 16" barrel significantly louder than 18 or 20? Noise is an issue with the kids, but so is weight.

Does it matter if it is 5.56 or 223 Wylde if I plan to reload varmint loads? This is my biggest question, since it seems like few people on the AR groups reload. I am more usually more interested in good groups than looking cool.

How can I save brass? I hated shooing my 1911 because I lost so much brass. Do I need a special feature on the upper receiver to add a case deflector? Does it beat up the brass?

Should I buy a cheap 16" for the kids, and save up for a varmint style upper for me?

I'm sure I'll think of more questions. I don't feel like I speak the same language as the folks on the AR groups.

If I were buying one for the kids to shoot.....

buy a S&W 15-22...they will have more fun with it.....

Much cheaper to shoot...then get your better varmint upper....

My AR is an AP upper/lower..Shilen SS 300 BLK 16" tube....

Vortex Stike Eagle & Stoner mount...here's a smokin' upper deal

https://www.midwayusa.com/product/6...ly-556-16-barrel-with-15-m-lok-handguard

S&W M&P 15-22

https://www.budsgunshop.com/catalog...ort+10208+22LR+16+Collapsible+Stock+25+1

That M&P 15-22 is already on my radar. It is very light and handy, I think that is the answer for the smaller kids. OK, me too. We have a pink Cricket 22 that is one of my favorites.

They have bags that mount on the Picatinny rail and will catch the empties, but they hang off the side, catch the wind, and generally screw up the handling. You can buy completely prepped military brass for a dime each. At that price you can afford to lose a few. If you want to shoot tiny groups instead of look cool, reload.

I cringe when I hear someone mention "cheap barrel".

To answer your questions:

- A 16" barrel is just as accurate as 18" or 20". The difference is velocity, not accuracy. It's worth buying a good barrel if you're interested in accuracy, but even mediocre AR15 barrels these days shoot as well or better than yesteryear's hunting rifles, in my experience.

- I wear ear protection when I shoot (if not using a suppressor) and don't notice any difference in noise between 16"-20". They are all loud.

- Generally speaking a 223 Wylde chamber will be a little easier to develop accurate loads for, but either can shoot really well.

- To save the brass, install an adjustable gas block and tune the gas system correctly. You'll find all your brass laying in a nice little pile at 3:00-4:00 to your right. On that note, expect most "off the shelf" barrels to be a bit overgassed; this is so people can run cheap ammo in them without failure to cycle.