Yes I work on projects with activities related to the versions.
For each version I realize the task 1, 2, 3, 4, and I deliver the milestone 1, 2.
From the start I want to create a template that can be copied 1, 10 or 20 times.
As you describe it, it seems you may use template project copy option : a version could be a sub-project, including tasks, milestones and links between these elements. Then you just have to copy the project, including the structure, to copy all the needed tasks.
For the same project a resource can work on multiple little activities (analysis, script writing, peer review ...) which is calculated in hours.
I wish I could give the possibility to enter hours in some projects
It is not possible to mix days and hours input : it would lead to unavoidable rounding errors. But even for small tasks, input in days can be less than 1 : 0.5 for half a day, 0.125 for 1 hour.
My advise : dont' follow up very small tasks : you will spend as much time to follow them than to realize them, and moreover you will never be able to plan them. One good compromise can be to define one gathering task, with some workload for instance planned ad fixed between dates, define your small tasks under this one, just to follow up the status, and input work on the gatering task.
On the Gantt view is it possible to hide the black bar (duration of the activity) => Option ?
I don't understant. Which black bar ? Any print screen to help ?