I'm putting in a radial system for my inverted-L and am wondering if the hobby wire like the kind sold at Hobby Lobby or Home Depot for hanging pictures, which is 22-24 gauge copper or aluminum, would work for radials? It's cheap, and I already happen to have a bunch. Thanks.
Sure it will work. Metal wire is metal wire. The electrons don't care about the packaging.
24 gauge wire is thin enough you might be concerned about the resistance of the wires, which will decrease antenna efficiency. Use some RF resistance calculator to get some estimate of the resistance, and remember if you have 16 radials, then the effective resistance is 1/16th that of a single wire. As a rule of thumb, I'd suggest aiming to keep the total resistance under 5 ohms, which should be no problem given a reasonable (at least 16) number of ground radials.
If you're going with elevated radials then you might have far fewer of them: in that case maybe you want to twist several strands together to effectively make a thicker wire with less resistance.