How many pockets do they have?

8 pockets if you include the top openings on the cargo pockets (for cell phones & such) that quickly stash things behind the pockets.

Does anyone know what the closure is

Button waist, zipper fly, velcro pockets. Pockets are too small for my taste.

The pants I'm wearing right now, are a size 44W but when I use the measuring tape, it seems like the pants have 49"W. How do I choose right size?

If you have more than 1 size 44W pants which fit you now, I'd suggets going one size larger in these. These slacks are less roomy than Wrangler's heavier-duty cargo pants AND these have a shorter waist...if you hike them up to have your belt just above hips, the inseam will be pulled-up right under your bum. If you have great legs, no problem. I much prefer the heavier and more roomy Wrangler Riggs Workwear Cargo Pant, although, for summer these lighter-weight pants under discussion would be better for casual use. The full-size belt loops are a positive thing for me. For any of the Wrangler pants, the "ripstop" models (certain colors only) are superior to the regular cotton fabric. Ripstop liiks and feels better and I believe is more durable.