I would start out one a day and eventually move to 2-3 per day. I take mine with meals(per my naturopath), however it is recommended that you take them between meals.
I would do 1x per day for first week, and then 2x per day second week, and 3x per week after 3-4 weeks (or something like this, you can do whatever you want of course).
The one I take is called HMF neuro and contains 12.5 billion probiotic (5 strains); it is the only probiotic that contains human micro flora which binds to your intestinal walls (supposedly) better than any other probiotic. I might get some megaflora soon myself though to mix it up. HMF forte is a prebiotic that you can take before a probiotic (don’t have to of course).
You might want to stock up on a few different kinds in one shipment or a few bottles so that you can maximize the $20 refrigeration shipping charge.
For maximum success, alternate the brands of probiotic you take to get different strains in your gut.