Sorting, Slippage, and Dependencies

New customer; setting up first projects, and having some questions. Every software package is different, so please don't take these as "intervals should have these features" but rather as "how do I do this in intervals?"

1. How can I have project tasks appear in a certain order? (i.e., the first task that needs to be done first, etc.)

I'm seeing two ways to do it now, and not sure if there's a better one. The goal is for me to see the things I need to do before I can do other things in that order.

a. Enter the tasks in the correct order.
Problem: If a new task is identified during the project, I can't get it into the right order.
b. Enter a number in the title then sort by title.
Problem: Same thing - if I have a new task, I have to manually renumber all remaining ones.

2. I know that philsoophically you don't support dependencies, though I'm not sure why. How should I be thinking about the task list for a consultant who has to do 8 tasks for a project, but three of them in fact depend on the completion of three other tasks in order to start them? or a situation where it is not exactly a dependency, but the logical progression of work would be to complete one before starting the next? Won't he wind up with a task list that has 8 items on it when there may only be 2 or 3 that he could really work on today?

(is the solution to make all dependent tasks low priority, then filter to not show them?)

3. How is slippage handled? One of the major things I need to know is whether slippage is occurring in my projects. If a task was scoped as 8 hours, and a person has put in 4 BUT they are only 10% complete, then I really need to know this. How is intervals used to let me see that important piece of information?

I would also like to know how this would work. Some tasks need to be completed in order. We would also like to seen them in a timeline form. Am I doing something wrong?