It is indeed easy to find all of the ISV solutions available as per your requirements. However, before selecting an ISV solution, consider the following points:

• Build versus buy analysis: Sometimes, going with an ISV solution may look like a quick win. However, it comes with a cost. When evaluating the cost of the ISV solution, you must consider the total cost of ownership and not just the cost of licensing. Others may include code integration, support, training, and so on. High-level estimation on the original requirements and gaps can help you to evaluate the cost of building these customizations yourself and compare that with the cost of an ISV solution in the long run.
• Benefits and percentage of fit: Understand all of the benefits that the ISV product has to offer and identify the rate of fit that you have with the requirements. If you still have to customize for more than 20-30 percent of the scenarios, you may be better off building the whole solution by yourself.
• The readiness of the One Version model: The ISV product must follow the Microsoft One Version model and continuously update the story. With the One Version model, the ISV solution provider must ensure the compatibility of their solution with the latest version of the Finance and Operations release.
• Product roadmap: Understand the product roadmap and features. Make sure that these deadlines are mentioned as part of the contract. For example, ISV currently provides tax calculations only for the US. However, Canada is on the roadmap. Make sure that you understand the deadlines for Canada and have those documented as part of the contract to ensure that your project doesn't suffer due to delays from ISV. Also, review the roadmap for the upcoming cumulative updates.
• D365FO release plan: Be aware of any new functionality that Microsoft is working on for new releases. You can find the features that Microsoft is already working on in the Dynamics release plan documentation (https://docs.microsoft.com/en-us/dynamics365/release-plans/). Will these features replace the ISV solution? How easy would it be to upgrade your solution and take advantage of the new features? Would it be more cost-effective? How will it affect the business if you wait for the new features versus if you do temporary customization or implement the ISV solution?
• Architectural review: Have detailed architectural reviews done by the technical architect on the team as part of the evaluation to ensure that there are no architectural gaps and that the solution is scalable.
• References: If you don't have an existing relationship with the ISV, ask for customer references, and discuss the recommendations before making a decision.

• Company size and support: Evaluate the ISV solution provider's size, financial strength, and any risk associated with the long-term support of the product.
• You don't want to involve too many ISV solutions as part of the overall solution. It will increase the dependencies for upgrades and take away time from your core implementation team in managing conflicts and testing.

After evaluating the ISV solution, let's assume you have decided to pick the ISV solutions that are best suited to address all of the solution gaps. Let's now discuss what you should do after selecting the ISV partner.