Re: Need help with some direction.
You asked if those bikes can handle the bigger tires. You probably won't be able to know until you see it in person. You have to measure the chain stays (the tubes that go from the pedals to the rear axel) where the tire is to see if there is clearance. If and when you buy a beefier tire make sure to buy a good quality tire that can handle a higher PSI so you can inflate it higher to handle more weight. Just like the rims you should be ok for a while on the stock tire and upgrade when you can.
As far as the brakes you will be ok. I rode a friends cruiser that only had a coaster brake in the rear and no front brake. I would say that was a little scary and I weigh 180 pounds. The bike you are looking at has front and rear brakes and they are v brakes which are better than coaster brakes. Just make sure the brakes are adjusted properly. Also be a defensive driver and always be scanning ahead for traffic.
I have heard of people's chain tensioners moving into the spokes. There are two good fixes. One is to wrap a thick rubber band around the frame where the tensioner is so it will grip the frame better, the best rubber I have found is what they use in the medical field as disposable turnacates. you can also use a couple of broccoli rubber bands. The second way to solve this is to mount a better type of tensioner. There is a sticky thread in here that shows pics. Just look up chain tensioner. Some guys have drilled a small hole through the frame and tensioner and put a screw through them. This is not the best because it weakens the frame.