Membership Dripped Content And Subscription Periods

I did the Wizard and setup for levels using a single dripped content subscription.

I am a little confused with the different modes and Pricing.

1. Do I set the time period of each subscription from here? http://screencast.com/t/JInhmuD0

2. Assuming I use the Period option to set how many days a member stays at each level, then what mode would be correct for what I want?

I want each member to start at level 1 for 20 day, then move to level 2 for 20 days, then level 3 for 20 days etc.

I want them to pay me a single payment for all the levels upfront. The subscription will have to be renewed after 1 year of service.

What 'Mode' would I use for each subscription?

I want the members to have access to all the previous levels after they complete the dripped subscription. So i want them to still be able to access the previous levels after they move to the next access level.

So what should my settings be?

I read about the dripped content in the manual but the manual does not explain what each level should be for this setup.

I hope you can help me with this.

Thanks