RE: How to avoid the rubber ring on the spinner
I haven't had the problem since I switched to aluminum spinners. If any ring is left behind it wipes right off, but usually there's next to nothing.
There are spinner cones made of different materials, but I've just used the cheap-o's so far.
Also proper tuning and priming. If you're needing to hold the starter up to the cone for any period of time, something's not right.