Shotguns are generally fine with all types of ammo ... no special barrel needed. A barrel with a changeable choke tube allows for a quick change choke. Never had much use for rifled slug barrels, I just used buckshot for larger game. Pumps cheapest, Mossberg 500 and Remington 870 good, cheap.
IMHO — The best, most popular 22LR, is the Ruger 10/22. You can get good 25 round mags. I had one many years ago and shot it as my learner gun. Still the best today. Reasonably good enough accurate.
If I fire slugs in my Mossberg 500, should the choke tube be removed first? If not, does it make any difference which tube is in place when firing slugs?
Thanks for your advice.