Identify where money or time is being lost
If missed follow-ups, sales opportunities and proposals are the main problem, start with the CRM path. If invoices, expenses, reports and financial records are the problem, start with accounting. You may eventually need both, but buying both before defining the workflow adds complexity without guaranteeing a better outcome.
A one-week test can reveal the priority
Choose ten recent transactions. For sales, track source, stage and next action. For accounting, track invoice, payment, expense and report. Give priority to the system that removes the larger measurable loss of time or money. Record that result before comparing subscription prices or promotional discounts.
Integration follows a clear primary system
Check the official integration or API documentation, cost and limits before depending on it. The presence of an integration name does not mean every required field is exchanged. Test with non-sensitive sample data and inspect duplicates, currency and tax mapping, ownership and access permissions.