How can I get a paid membership upon expiration to revert to the free lifetime membership access?

You can't unless the free plan is a parent of the paid plan. Users with just a parent plan always revert to the internal free lifetime plan. Currently you can't select a fallback plan, but such a feature is planned. They also shouldn't lose access unless you have free registrations disabled within CBSubs > Settings > Global.

Also once an account has expired, how would an end user go about renewing their membership when they have no log in access?

When they attempt to login it should ask them to renew or upgrade. So ensure the plan can be publicly accessed.

Also I should note that curious enough I can not access CBSubs support forum as it says i need a membership.

You don't have a CBSubs subscription. You have a Developer subscription, which has higher priority. So you'll want to always post here.

So until there is an upgrade that allows a fallback plan, if I move my paid plans under the parent plan of lifetime free, then it would default to the settings I have set up for lifetime free?

Yes, they'd have all the benefits of the free lifetime plan plus whatever plan they paid for. When the paid plan expires they'd still be a member of the free lifetime plan. This currently is one of the only ways to accomplish this. The alternative is have all plans, except the free lifetime plan, as non-exclusive parent plans.

If I changed all my plans from exclusive, could I set up the system to give every paid plan a free lifetime plan as well?

If all plans, except your free lifetime plan, were non-exclusive then they're be required to have the free lifetime plan. They then can add the other plans onto it. Depending on your needs this could be good or bad.