Hi Andria,
1. Yes, you would use the test merchant email and the test account PDT Id
2. I'm not sure it needs to be configured because I think we pass the return url to paypal, but you could enter it as http://yoursiteroot/Services/PayPalReturnHandler.ashx
3. Shared SSL typically uses a different host name than the main site and will therefore probably will not work with mojoPortal's google checkout integration, however, for PayPal Standard SSL isn't needed.
If you test with PayPal production and use your own account and process the smallest possible order ($1 I think), the only cost to you is the paypal transaction fees for the test transactions, the rest of the money goes into your own account so the cost of testing is like 35 cents per transaction. I realize these are hard times, but if you factor the time and frustration saved into the equation it may be worth it for most people. Just saying if you have no luck with the sandbox, my experience is that production works as expected and the sandbox is a royal pain. Ultimately I think one should at least run one real transaction through the production side to make sure it works before having a real customer come along and have it not work.
Hope it helps,
Joe