Elissa,
You should find all four of your days to be roughly similar in crowd size, even though your arrival day is a weekend day. Pretty light crowds overall!
As to what parks to go to on what days, here is what I would do if I were staying at a Disney Resort (taking advantage of the Extra Magic Hours), and if I wanted to do 1 park per day;
- October 4 - Magic Kingdom
- October 5 - Hollywood Studios
- October 6 - Animal Kingdom
- October 7 - Epcot
If you write me back directly with more information, I can provide more detailed suggestions. Some things that might change your daily park selection would include arrival and departure times, if you are staying at a Disney resort or not, if you have Park Hopper ticket options, and if you really want to go to all four parks or not.
Glad to help with any follow-up questions, including restaurant suggestions!
Have a magical vacation!