Can I customize the bottom navigation bar?
Yes, for free. Long-press any tab to open Customize bar or Hide bottom bar, or find both in Settings under Customize Kinoku.
Yes, and changing the bar is free. Long-press any tab in the bottom bar and a small menu opens with two choices. Customize bar takes you to a screen where you drag tabs into a new order and add or remove them, with room for up to five tabs. Hide bottom bar takes the bar away for a cleaner screen.
While the bar is hidden, a small pill with an up arrow sits at the bottom edge of the screen, and a tap on it brings the bar back. The same controls also live in Settings, under Customize Kinoku, where the Bottom Navigation Bar switch shows or hides the bar and Customize Navigation Bar opens the tab editor.
The Today tab cannot be moved or removed, though you can arrange the rest around it. On the free plan, tabs for Pro screens carry a lock in the editor, and tapping one shows what Pro adds there.