I am about to purchase an email list of over 100,000 contacts. Before I do I wanted to know if their is any kind of limit in Sugar as to the max amount of emails it will process.
Sugar itself does not have a hard-limit to the number of emails it can send, but your SMTP Server may have a limit. As an example a free Gmail account will only allow you to send so many emails, I do not recall the exact number, over a 24 hour period.
To ensure that your Campaign is sent in a timely manner, I recommend reviewing the following Knowledge Base articles:
As an Administrator, you can modify the Campaign Batch Size and the frequency that the 'Process Nightly Mass Email Campaigns' Scheduler runs, in order to send more emails in a given period of time.