For me my tablet had built up skin oils over the year so the paper was a major difference. Software wise I personally like my digital art to mimic traditional mediums, so I use Corel Painter. I've never used Paint Tool Sai before but I hear people love it for line work. So it should work just fine for most of what you're after. Landscapes might be a bit harder I don't remember seeing any done in Paint Tool Sai but I could be wrong.
For me my tablet had built up skin oils over the year so the paper was a major difference. Software wise I personally like my digital art to mimic traditional mediums, so I use Corel Painter. I've never used Paint Tool Sai before but I hear people love it for line work. So it should work just fine for most of what you're after. Landscapes might be a bit harder I don't remember seeing any done in Paint Tool Sai but I could be wrong.