I have a doubt. After the one-year subscription period, if I do not renew, I lose the PRO features or just the future updates?
By having the free version of Infuse installed (with or without Pro) you will always have the latest and greatest version.
Whether you have the Pro features or not is simply determined by whether your subscription is active.
With the standalone PRO version so I have all the PRO features forever, without a future upgrade to version 6?
Right. With the standalone paid app you would always have Pro, and you would receive all v5 updates (5.1, 5.2, 5.3, etc…). Infuse 6 would be a separate purchase whenever it becomes available.