I am just hearing about Yahoo Sandbox for the first, I personally do believe that Sandbox effect exists Yahoo. I dont have such experience with Yahoo.
Not really because as soon as the web pages are indexed and start receiving links, you may find them in the Yahoo listings.
Not really - just focus on quantity of backlinks and build social media profiles and pages as well as utilize the yahoo sm webmaster central
Never heard of a sandbox in yahoo but that might be because i focus mainly on google and yahoo just seem to follow suite.