Magento HTTP 500 and redirect fix and small updates (URGENT)

**Please do not apply for this project if you cannot do this within the budget.** We finished developing a Magento shop and now want to move it to a new domain name. I've just moved all files to the new domain and also imported the database.. but somehow it redirects me to the old site and when I reindex and flush the cache, it gives me an HTTP 500 error. I'm looking for an experienced Magento developer who can help me with the following: 1. Fix the redirect and HTTP 500 error for me and let me know what exactly was wrong so I can fix this in the future. 2. Update Magento Blog extension to the latest version. 3. Make it so it's required for visitors to create an account before they can place an order. 4. Clear all current orders. If you have any questions, please let me know.