Thanks for the responses. I will write to ANA to see if they have an interline agreement with Silk Air. The United flight is the second flight (NRT to SIN) so I'm not sure if it will be helpful to get info from them.
On the second issue, I am going to ask the transit hotel in SIN if they will hold a bag for me because our return is also through SIN so the second issue might actually work out that way.