I'd say go with the Threelac. I know I keep talking about it but I ate molasses sweetened cookies (a whole box) and didn't get sick. Before I took Threelac if I did that I would be riving on the floor with various symptoms.
Threelac is a probiotic and therefore you do not need to take another one. But what is very important to take is a digestive enzyme complex that contains cellulase to eat up dead yeat. I also take olive leaf extract. Some say it is not necessary to take anything else in addition to the Threelac but I'm taking that just in case (Olive leaf extract is also know to boost immune system functions). The other thing to watch out for is your liver. Your liver ends up having to process all those toxins from the yeast die off and if you are like me you got your candida from too many Antibiotics . I take Smartcleanse by Renewlife which is a system to cleanse both your colon and liver. I found that completly took care of the constipation that accompanies Candida. I also just started doing Cod Oil packs and will do a "liver cleanse" when I finish taking the Smartcleanse.
To answer your question about how much to take I would start with a one pack for a week to see how well you tolerate it and if no problem move it up to two then three, etc... (they recommend moving up to 5). I am at three now and will move up to four next week.