My first AR is a Stag and I love it! I did build mine from the bottom up instead of purchasing a complete AR. I wanted to know the internal workings of it and plus it was a fun and educational project!
I did get an Aimpoint for it the same time I finished building it. But I didn't mount it on until I shot it for a couple weeks with the iron sights I had purchased for it. I think it's good advice to learn how to shoot your rifle using the iron sights, but no need in waiting thousands of rounds just to buy a red dot.
If you have friends that have red dots, try those out. If not, go to a gun range that rents and see if their rentals have red dots. While you are narrowing it down on which optics to buy, learn your iron sights! That way if you ever come across a situation (hopefully you don't) where your red dot is in operable and have to depend on your iron sights, you'll at least know how your gun works.
That's just my opinion...My AR is more for paper shooting and having fun with it, than for personal defense. It's hard for me to justify my AR as my PDW, since my XD is so easy to carry around every day, and fits perfectly in my night stand drawer. IF ever comes a time where my AR is my only weapon to use for personal defense, I feel confident enough to know that I can use it with or without an optic because I know my iron sights are there.
BTW, I don't have my aimpoint anymore and upgraded to an 4x32 ACOG (TA31). I was going to go with the 3x magnifier, for my aimpoint, but after shooting my brother-in law's AR w/ an ACOG and looking at the cost of the total package of the aimpoint w/ the magnifier, I decided to sell the Aimpoint and put those funds towards the ACOG. So far, after shooting around 300 rounds through it, I don't regret it! Now, I'm just waiting for my red dot to mount on top of my ACOG for those targets that are closer (it probably would've been more fun building another AR thats set up for close quarter shooting, but there's already another project on the way)

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Ultimately, what I'm trying to get at is, try things out before you buy. You will save yourself some $ by doing that! Some people are perfectly happy with nothing but the iron sights, and some (for the most part most enthusiasts, including me) want the red dots for the cool factor!