Hi,
Amiga power supplies and cabling can be found easily.
If you are sent your Amiga by post, because of the shocks the floppy drive may arrive damaged, so it may be a good thing to ask your seller to ship the Amiga with a floppy disk inserted. As I'm not a specialist, I count on other posters to confirm this.
Some games of the 80's (and maybe the early 90's) won't work properly or work at all on the Amiga 600 and 1200, even with tools like WHDLoad or degraders. So if you want any old game to work properly, you must use an Amiga 500 (not 500+), 1000 or 2000 with Kickstart (the ROM) version 1.3. If you want to play AGA games, that is games designed for the Amiga 1200 and 4000 graphic chips, which are in a minority, then you must have a 1200 or a 4000. If you want to play AGA games and as many older games as possible, then I recommend you to buy a 1200, because it is usually much cheaper than a 4000. In addition, the 1200 is not much more expensive than a 600, compatibility issues are not significantly more numerous than with a 600, and it is more powerful and upgradeable than a 600.