[Zachery]

Assuming you're set on going to 5.

I would first make sure you have a upgrade plan, what you're replacing the addons you deem vital to your site and how you're going to get them working/compatible with 5.

Assuming you do get that out of the way, your next step should be removing vBSEO and redirecting all of the current rewritten urls to the defaults.

Once you're on the default urls for a bit 1-3 months, I would carry out the upgrade to vBulletin 5.

Test, test test test, test some more, test again, keep testing.

If this site is important to you, do as much prep work as you can, prepare your community for the change, explain why its going to be worth it to upgrade.

You'll still lose some people in the transition, but as long as you've done your best the site should be fine going forward.