Magento Upgrade and Trouble shooting

I recently tried to upgrade from Magento version 1.7.0.2 to 1.8.0.0 ([login to view URL]) and of course the upgrade did not work properly. The admin side still shows it as version 1.7.0.2. and I have found the following errors/issues within the admin section: 1. System > Magento Connect > Magento Connect Manager gives a "Sorry about this" error page on my site. 2. Sales > Orders does not display any of my orders. This can be fixed by enabling the 3rd party module Aitoc_Aitpreorder All of my products, customers and order (new and old) are still there, so the data has not been lost from the database and the transaction processes are still working correctly. On the front end I'm having the following issues. Using the default Magento theme, there is no product information on the product pages. They show up on the category pages, but there they do not show the prices (I'm not 100% sure they should with the default theme though). If I have that Aitoc_Aitpreorder module disabled (so that I can see the orders on the admin Order page), then only one product shows up on the category pages and there is still no details on the actual product page. So this module is no longer compatible with whatever mixed version of Magento is running on my site. They do make a 1.8 version of that module, but I've not bought and installed it yet do to the other issues. If I try and enable my 3rd part theme, there are all kinds of odd issues. I am looking for someone to successfully upgrade my site to Magento version 1.8.0.0, get it working 100% correctly with the Default theme, and remove the 3rd party models and themes (I will reinstall the new versions of these later). Successfully completing this job on time and on budget could very well lead to routine upgrade work in the future.