If you don't plan on making videos with the AGA chipset then I'd recommend getting a PAL A1200 and a US Power Supply for an A500. (The A600 power supply that comes with an a1200 is crap and if you get a PAL system it will probably run off a 220 volt 50Hz outlet.)
You'll need a PAL-capable monitor such as a Commodore 1084 series to display anything in color but I wouldn't recommend using the built in tv connectors anyway due to electrical interference on the motherboard itself.
The reason I recommend PAL systems is because they are cheaper and most classic Amiga software runs in PAL resolutions anyway so it will save you the trouble of having to "PAL Boot" your system with a patch to get the software to run.
If you can't find a PAL monitor and are out of options then you can get a scan doubler and hook it up to a VGA monitor but scan doublers are expensive and also hard to find.
If all of this sounds like a major headache to you then you might want to consider the cheaper option: emulation. You can run most Amiga software on Macintosh by buying the
Amiga Forever CD and then download the latest version of
EUAE and try to follow the instructions for setting up EUAE. It is a little more difficult but it will work on most modern hardware.