Generalizations.
It is better to buy a used quality rifle, than a new less quality rifle.
Truth. ....though defining "quality" can be problematic......
The lighter the rifle the more you will carry it.
Only true for lazy people .... which is 90+ percent of Americans.
Iron sights work, spend all the money on a rifle this year, get a scope next year.
Iron sights work, but a good scope works better in low light and at longer ranges. True, but if you can't hit a deer's vitals at 300 with irons ( provided you did your due diligence and practiced at that target size and range), I'll bet dollars to doughnut holes you can't do any better with a Swarovski or Zeiss, either.....
apparently misunderstood your reference "$150 Mosins". I thought you were indicating that a $150 Mosin would be a good option. I happen to like the rifle. A lot. But that's me. ]
Don't get me wrong, now: A 150 dollar mosin that will shoot to 4 MOA
will be more than sufficient medicine for any sized bambi (or even elk!) within 100 yards of the shooter, and still have 4" of shooter error to spare! If the Mosin weilding hunter were really determined, and took up handloading, tuned his rifle, etc, it would be more than enough to 3-4 times that.... after that, he'll have to sart reading the wind/mirage and might
need optics........ but for 85% of North American big game hunting (and 98% of it east of the Mississippi) a properly stoked 91/30 would work!
The bigger the bore the less shots will have been put through it.
Depends upon the wallet size and the level of masochism of the former owner, but in general true: I have ben advised against buying a varmit caliber rifle (.22-250 IIRC) just on the GP that it had probably had a bajillion rounds shot at prairie dogs out of it, and likely less maintenance than would be due such a round count.......