Rewriting the clover-android-sdk in C# sounds like an exercise in extreme pain and in order to do it you'll need to learn a lot about java and android. Also what happens when Clover updates the clover-android-sdk.
If you decide to go with Xamarin you are also unlikely to get much support here.
I tried to create Xamarin Binding lib from Clover Android SDK and got tons of errors initially so did not attempt to pursue it at that time (which was a couple of years ago now) but I would be
very interested to try to help get something like this going as we definitely have uses for it (main use case would be integrating our in-house gift card server into a payment flow process so that the purchaser can run their gift card rather then the cashier running it through the semi-Integrated Windows POS)