There are a few different versions of Marketing Cloud Account Engagement powered by Pardot, but for small to medium businesses, the Growth edition should provide you with everything you need to get started.
If you want to use Google AdWords and attribute which keywords provide the largest return on investment, consider paying extra for this feature.
Pardot offers standard reports, but if you want to create customisable reports to obtain greater insight into your data, it’s worth considering buying the Plus edition that includes B2B Marketing Analytics.
If you want your sales teams to have greater visibility of customer engagement, then you may also want to consider Salesforce Engage, however this is at an extra cost per user.