Since you mention piggyback, I assume the mount is sorted.
For starters, I'd try the lens wide open. 1 minute should show something assuming the background is dark enough. ISO1600 is reasonable. When you start, take test shots and see how it goes, and don't be afraid to adapt as necessary. If you can afford longer exposures, that's worth a try. Individual exposure length gets you more faint stuff. More exposures help reduce the noise. If you're going to do darks, take at least 10 otherwise you're potentially adding noise. If you feel you're getting enough light, you can stop down if that helps with the lens performance, but be aware if the aperture isn't round, you will get diffraction spikes around stars.
From random notes I tried f/2 ISO1600 in the past, sample results at viewtopic.php?f=22&t=28479
Note they're processed somewhat heavily due to light pollution. Without that, you should have a much easier time of it than I did.