>>64100497 (OP)
3" barrel is the smallest I'd recommend, but if you got it already you'll be fine
.38 special is the best round for plinking and fantastic for self defense
The short sight radius and lack of adjustable sights will hurt you a bit, but you'll learn quick what each load hits at
For protection ammunition, get the standard pressure 150gr wadcutter from Buffalobore
The .38+P really doesn't do much more, and kicks like a mule in a little gun.
868 fps (251 ft. lbs.) -- S&W mod. 60, 2-inch barrel
890 fps (264 ft. lbs.) -- S&W mod. 66, 2.5-inch barrel
961 fps (308 ft. lbs.) -- Ruger SP101, 3-inch barrel
1005 fps (336 ft. lbs.) -- S&W Mt. Gun, 4-inch barrel
The hardcast wadcutter leaves a massive wound cavity and penetrates deep