Well anybody can do a heat scan on your house, but I believe that they can't use that specifically to get a warrant. But I wouldn't be concerned at all with only five plants. Now to your second question, plants in veg will supposedly eventually show preflowers, I'm sure how long it takes, maybe a month or so. Somebody should back me up on this if I'm right, but my impression is that you can either wait awhile in veg to see preflowers, or you can clone your plants and flower the clones, as the clones will of course be the same sex as the clone parent, but I do believe that it is not the best idea to flower plants and then return them to veg, as it supposedly slows things down quite a lot.