Drupal Error and Security / functionality Upgrades

I have a site that I acquired as an investment a year or so ago that runs in Drupal. Recently the site has broken with a template related error that I cannot fix. In addition the site is receiving an increased amount of spam that I need to understand how to remove and block. I also need the site upgrading to include latest security patches and optimally configured. The Drupal installation could also do with a detailed inspection and any other broken functionality restored. The main priority is to fix the site then work as above to remedy other issues.