When creating a test plan, the order of which the test cases are displayed matches the order set in the Test Suites and Cases section.
This is not entirely desirable if you want to create a very specific test plan / script, such as a smoke test which aims to cover the main functionality of a product in the smallest amount of time as possible.
My suggestion is that as well as allowing the user to specify the order of Test Suites, but also allow the user to specify the order in which the test cases are ran within the test suite (drag and drop when selecting test cases etc).
Another benefit of this is that within the section of adding a test result, you could select “Next” to move to the next Test Case in the List, rather than relying the user to go back a page then add another test result.
A possible work around is to pre-order the test cases when managing the test suites, but test suites are like a library of tests. If you ordered your test suite to match a test plan, then another test plan which follows a completely different order of tests would not work.