Even if they are not transferred, you can always add them again. The only savings to consider is changing to your new base plan at the end of your billing cycle. 

Yes, absolutely! Your boosters will be valid with any of the prepaid plans.

I have changed my husband's base plan 2 times and the boosters have always been retained. If for some reason they were not, you would have to get hold of Koodo to re-add them. Just watch the date you change your base plan to prevent paying twice for the same month (eg: if your base plan renewed on the 1st and you decided to change the baseplan on the 2nd, you would be charged on the 2nd for the new base plan). 

I always took a screen shot of the existing boosters before switching just in case.