If you're using CBSubs Mailer it should send based off the expiration date so it should be before the grace period. If you mean the presentation/CBSubs Email emails then I believe they'll send when the subscription is actually expired (after grace period).

No, for those you don't need to do anything special. They send on plan state change. You may want to setup CRON for expiration's though or you'll need to regularly visit CBSubs backend to trigger expiration's. See your CBSubs documentation regarding this as CBSubs > Settings > Global for the URL.

It'll send the expiration email when the subscription expires, but a subscription won't expire unless you trigger expiration's. By default this is done by visiting CBSubs backend. It can be configured further within CBSubs > Settings > Global, but it's best to do it via CRON and trigger the URL provided in CBSubs > Settings > Global regularly (once a day for example).