Do I turn off time machine when adding Mojave and then turn on after downloading.

You can look in System Information, or use an app called Go64.

To get to the info in System Information, hold down the Option key and choose System Information from the Apple menu.

Click on Software, then Applications.

Click on the Intel 64-bit column to sort by that. Look for the No's

Uninstall the programs before upgrading as uninstalling after may prove difficult if the app's uninstaller is also 32-bit.

No, it's not necessary.

You're welcome. Just be sure to do a full backup before you install and check here for any incompatible apps you may have that will not work with Catalina:

https://roaringapps.com

64-bit apps will not be affected in Mojave. The link I gave you will check any third party apps for compatibility in Mojave.

https://roaringapps.com