Joomla 1.5 site needs optimization

My site was migrated recently from Joomla 1.0.15 to 1.5. The site is working but not 100% and it needs some adjustments. The person who made the migration hasn't finished the work and disappeared. The main problem is the server, which has been crashing sometimes. My webhost says that this is happening because there are some files missing. I need someone that is an expert in Joomla to make the new installation of Joomla 1.5 work in an optimum way. I'm willing to pay by the hour if the person qualified to do this job would prefer this kind of arrangement.