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Set all custom fields that you may need in your Deals, including such fields from CRM as Company, Contacts, Transactions, Products.
See: Setting Up Issue Custom Fields,
Setting Up Custom Directories (Dictionaries)
That's how your Deal can look like:
3. Set Sale workflow
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It's possible to display list of Deals in customer card, like there
See more: How to display list of issues at Company/Contact card?
5. Create Deals Dashboards