1. Create a staging/test instance with a copy of your current installation
2. While you said that you're using everything, once you've upgraded your test system to 4.5, just review your list of installed apps and plugins and see if you can just remove all the stuff which won't be necessary with 4.5 or if it contains some data which should be imported to 4.5 to not lose any important data. I have quite a huge list of apps and plugins which will become deprecated once IPS 4.5 is here and I've already started looking and planing the post 4.5 alpha phase, to provide ASAP upgrade routines for club pages, referrals, while other apps like my default guest language, just aren't worth the additional work to see if I'll be able to import the setting..
Also subscribe to all the files and support topics if you haven't already, to keep updated about the upgrade notices from the 3rd party devs;)
Anyway, what I'm trying to say is => Staging System is a must have, if you don't want to have your board down for days; and that each of such bigger IPS upgrades is also a great opportunity for housekeeping to remove some unused ballast 🙂