Upgrading a plain Plone Site works well.
Of course the best practice is to create a full backup of your site, or create a second installation where you can perform the update first. If everything goes well you can upgrade your LIVE site.
I guess you have some packages installed from the collective or other sources. Then you have to check if the particular package is Plone 4.3.2 ready. On well maintained packages you can get the needed information from pypi (further: CI server, github, etc.). You need to pin the required versions in your buildout manually.
Upgrading from Plone 4.0.x to 4.3 mainly addresses some deprecated imports (moved modules) and the by default disabled jQuery integration (jq instead of $). Those two points are the main reason why some upgrades in my case did not work well.
To make sure your 3rd party packages are ready for Plone 4.3 you can use the collective.ploneupgradecheck
(Also clone the source of the package you want to check)