I want to improve the way I organize my projects/tasks/schedule

What I do now is:

1. keep an excel sheet with the name of the most important tasks/projects, I look at it at the beginning of each day and decide the ones I will focus on
2. on iCal I write down events for each day, or for a concrete time (13 to 14 hours). I set up each day the tasks I want to accomlish, and allocate them hours
3. I use Things (culture code) to keep info about tasks and projects not very important and which are not time allocated yet (GTD name = someday)
4. I use Mail on Mac and create folders for the mails I want to process with the name of the different projects
5. I save the main info for each project on freemind maps

My system works well at the moment but it is pretty complicated to use. I want to make it better and I am looking for something with these requirements:

• must be 100% offline accessable
• it should use as less programs/resources as possible, ideally just one program should be able to manage all my info
• I can use the GTD methodology mixed with priorities and I can allocate each task converted to event on my calendar
• I can have different daily/weekly, etc views on a calendar to see the "big picture"
• must run on mac os x leopard
• price does not matter, I will pay for this

So, according to your experience, can you recommend me something like this?

Thanks