Connecting to SQL Server I currently have set the Server Role sysadmin on the account accessing SQL Server where I'm about to host Sitecore databases. My guess is that it's way to much privileges for the account, and really wonder if dbcreator would be the correct Server Role for the SQL Server account?
You are right, you granted to much privileges. You don't have to assign any server roles, but you should should assign db_datawriter, dbreader and public role memberships for your user to the web and master databases. You should also assing execute permissions on all the stored procedures for your db user.
for the core database, assign the following role memberships:
edit: most recent public installation guide that I found: https://dev.sitecore.net/~/media/Downloads/Sitecore_Experience_Platform/8_0/Sitecore_Experience_Platform_8_0/Non-secure/Installation-Guide-SC80-A4.ashx
The best advice is to follow the installation guide for your version, download it on https://dev.sitecore.net