That should work fine, Weemus. Having said that, software compatibility varies, so for a few programs you might have to try some versions. But an A500 with kick 1.3 is the closest thing to an A1000 (apart from an A500 with kick 1.2, of course), so there should be minimal trouble.
The latest version is Sonix 2.0 that you can get from PlanetEmu (click on Amiga, then Applications). There's a newer version of the playroutine for newer Amigas, but not of the composing software.