Concur fully with Jordan's above post. Chasing your tail missing small steel in real world conditions is ZERO fun. And you'll often burn all your ammo and go home with minimal confidence. Go bigger and thinner and less steel vs quantity and thickness.
I have a friend with a steel cutting company, so I've had him cut me a lot of AR500 for local guys around here. I've torture-tested it and shot the crap out of it. Unless you're shooting steel 200 yards and in with a super-velocity cartridge, 3/8" is your huckleberry. I'd only go to 1/2" if I intended to abuse it at close range. I find that 3/8" targets give better feedback visually, as they swing more, being lighter-weight, and also audibly since they have more of a ring than 1/2" targets do. Heavy bullets with a lot of momentum don't kill AR500 steel, velocity does. Big bullets may be hard on hanging systems, but the steel itself is fine, unlike shooting it with high-velocity impacts. We've tested the effects of .338 Lapua AI shooting 300gr Scenars at 2900fps on 1/4" AR500 at 100 yards, and it doesn't even dent the steel. After a while the target will dish from the sheer force, but the bullet itself doesn't damage the steel at the POI. I've also burned holes clean through 3/8" AR500 by shooting it at 40 yards with a 7mm 100gr Sierra HP from a 7WSM at 3700fps, while a 162AM at 3070fps just splattered, and a 140gr TTSX at 3300fps caused slight dimpling, when shot at the same distance. Speed kills steel. Keep your impacts under 2800 fps, and your steel will last a long time. Don't shoot it with steel-core ammo.
Unless you have access to private property where you can set up a bunch of targets, you'll probably find that you tend to use a half-dozen targets or less on a regular basis. I'd get a few different sizes between 8" and 18". IPSC shapes are fun, as are coyotes and other animal representations. I understand the appeal of trying to hit a small target, but if you're having a tough time, it's nice to take a shot or two at a bigger target to see what's really going on with your bullets downrange. A 3 MOA target is not too big for that application, while a 0.5-1 MOA target is quite challenging in real-world atmospheric conditions.