Keep in mind that some reports only allow breakdowns by campaign, such as Menu > Marketing > Email > Analyze. If you want these reports for certain emails, create your campaigns and assign your emails accordingly.
HubSpot has recently introduced campaign properties: Manage your campaign properties – I’d recommend setting up these properties to better sort, filter, manage your campaigns (e.g. by team, market, language)
Familiarize yourself with the campaign calendar. The campaigns tool can really replace other project management tools if you’re doing it right. Plan your campaigns with the marketing calendar
Try to avoid re-associating assets between campaigns. While HubSpot is now capable of carrying over historic asset performance from a previous to a new campaign, I remember some hick-ups a while ago, losing asset performance when associating it to a new campaign.