Will I lose my customizations if I upgrade to the Pro version of the theme?
The simple answer is no.
A thing you should check before you upgrade is if you have are using a child theme.
Also, if you've made changes done to the theme files directly, without using a child theme or a plugin, those will be lost.
Neve -> Neve Pro
Neve is a theme and Neve Pro is a plugin. Installing the Neve Pro plugin will not affect the theme settings.
Hestia -> Hestia Pro
Hestia and Hestia Pro are different themes, in order to keep the changes, install Hestia Pro as a new theme while Hestia is still active.
ShopIsle -> ShopIsle Pro
ShopIsle and ShopIsle Pro are different themes, in order to keep the changes, install ShopIsle Pro as a new theme while ShopIsle is still active.
This chapter of the documentation explains how to set the front page.
Zelle Pro (formerly knows as Zerif Lite/Pro)
The front page in Zelle Pro might work differently than in the previous/free version. Here is a guide on how to enable the built-in sections of the theme, on the front page.