My 2 cents:
You should check if the requirement for installing Integration Agent comes from being on a 10.5 or before or just from an old architecture slide mentioning Integration Agent instead of MSR.
If you can go for a 10.7, you should use 10.7. The reason for Integration Agent is having a local bridgehead for integrating to on prem systems while the majority of integration is running on IPaaS (webMethods.io Integration). So MSR fulfills the same requirements and a 10.7 MSR is better optimised in footprint than a 10.5 Integration Agent.
You may need to check your licensing though, if you already have a MSR license.
The ports can be defined/changed from default during installation. As mentioned before 5555 is the default port for all 3 products.