@jasonlav Thanks for reaching out! To answer your questions:
1. Based on the Yakima Support Site they should be compatible. It looks like you need a Landing Pad 1 in order to fit your Skyline Towers to your topper. Please note that those come in a 2 pack, so for two bars on your topper you will need to purchase two sets.
2. This will depend on the width of your topper, what you intend to put on your rack (will it fit), and how much you want the bars to overhang the sides. Yakima Core Bars come in 50", 60", 70", and 80" sizes.
3. See bullet number 1.
4. You should only need the Landing Pad, the Skyline Towers, and the Core Bars in order to get set up. We definitely recommend lock cores as well.
Hope this helps!
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