We can't tell you what gear ratio range (and therefore which chainwheel) will work with your unspecified cassette and your particular needs. Neither can we tell you which position on the spider will work without knowing your chainline. In fact neither may be ideal. Think about what gear combinations you used as a 2x10 and look up a gear ratio calculator, then look up info on determining and adjusting chainline before you make any more mistakes, as 1x cranksets designed for fixed/single gear bikes may have a different chainline than you need..