RE: How many times a week???
The way to lose a bit of weight off your stomach is a simple case of losing fat. You cannot spot reduce fat, so forget about specific exercises (200 ab crunches a day, all the fancy ab machines on the market etc).
Correct diet and regular cardio will reduce bodyfat. Of course, gaining muscle will also go some way to burning fat as your metabolism will increase the more muscle you carry.
Weight training three times a week is a good split - there's plenty of good routines posted on this site.
I would do some sort of low intensity fat burning cardio, three times a week. Or, possibly consider H.I.I.T. Again, plenty of info can be found on this site.