1) There's no way to know in advance or to get notified of ongoing promos. Keep looking on Koodo's site. There's been quite some promos last month that were on and off. Follow sites like RedFlagDeals which alert you of new deals (from mobile, to clothes and food)
2) No. 1) answers this question. There's no way to know in advance of promos.
Always check what you have right now and what you will get before switch. You might get a cheaper price with similar plan, but overage charges could be much higher. So you should see your Minutes/data usage in all.