Effectiveness of exercise form?

[Anpadh]

OK. I need to flatten my tummy, build some muscle and get some flexibility. I am not really looking for endurance and nor am I looking to get ripped. I am 50 and single, so all I want to do is to get in shape for health reasons, rather than to attract girls. I read somewhere that it is good to mix up the exercises so that the body does not get used to any one type of exercise. So, here's what I do -- crunches, stretching, and weights. For crunches, I lie flat on my back, and cross my ankles. Then, I go both ways -- lift from the waist, 25 times, and then lift my legs and bend at the knees, when they are over my stomach, 25 times. My question is: Do these exercises count as crunhches or do only push-ups count? Also, is touch-your-toes a kind of crunch? For stretching, I just lift up each leg, one at a time, until the heel is on my dining table. My table is 4 feet high and I am 5'7" (190 lbs). And I lift weights, but only a 5 lb. weight in each hand (25 times each hand). I grip each weight in my fist and let it hang to knee level and lift my arm to waist-level and let it drop down to my knees again. I do all of these exercises just once, each day. I take a day off each week but it is never the same day every week. The only cardio I do is a 6-mile walk each day (takes 90 minutes). Am I doing anything completely wrong? I read somewhere that it is better to do no exercise at all than to have the wrong form. But, I cannot afford a personal trainer. So, any advice?