Is it correct I need execute-right to change into the directory ?
 

I notice that when using ftp, I need execute (x) rights to be able to change into the directory.

Then I also need read (r) to see the files inside that directory.

Then finally I need write (w) to be able to delete files in this directory.

This execute (x) right to be able to change into a directory with ftp concerns me in that this makes it also possible to execute scripts and programs.

Only if the script or program has execute rights.

For executing scripts and programs, you need to set the individual permissions. As you have already noted, execute for a directory has a different meaning.

Thank you for clearing this out.

Execute for a directory is required for entering the directory or for accessing files within a directory. Even if you have just execute permission you can still access a file within a directory. r permission is required to ls in a directory but you need x for ls -la. If you have w then you will be able to delete any file in the directory, regardless of the permissions on that file itself. As said above, execute is at file level.